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1
Terzieva, Radoslava V. "Gas-phase chemistry in interstellar clouds /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488202678775902.
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MacKay, D. D. S. "Aspects of interstellar and circumstellar silicon chemistry." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337320.
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Brown, Paul David. "The role of grains in interstellar chemistry." Thesis, University of Manchester, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.668955.
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Marshall, Charlotte C. M. "On the diffuse interstellar bands and the local interstellar medium." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/40158/.
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This thesis presents results from four different studies on the diffuse interstellar bands and the local interstellar medium. Firstly, a detailed investigation into the profile of the λ6614 diffuse interstellar band (DIB) is presented, which was aimed at ascertaining the origin of the observed fine structure and overall band shape, and why both of these properties change between a number of different lines-of-sight. A new method for normalising DIBs is described, and revealed new information about how the λ6614 band evolves between lines-of-sight. Observations and modelling of the DIB profile towards HD 147889 suggests that this line-of-sight has the highest internal excitation of the carrier, which accounts for its greater width and additional structure. As a continuation of this project, a further fifteen DIB profiles were examined towards HD 179406 and HD 147889, some of which are thought to correlate with the column density of the C2 molecule. It was shown that HD 179406 and HD 147889 demonstrated almost identical band profiles for the ‘C2’ DIBs, which differed considerably to the ‘non-C2’ DIBs investigated in this study. Analysis presented in this chapter strongly supports the idea that the ‘C2’ DIBs form a distinct class, and the normalisation method used provides a new criterion for validating whether a DIB may be classed as a ‘C2’ DIB. A study of small-scale structure in the ultraviolet (UV) region towards three stars within the ρ Ophiuchus system was undertaken using observations from the Hubble Space Telescope, to deduce column densities of atomic and molecular species, and to obtain physical parameters such as density and kinetic temperature through chemical modelling. The biggest absorption differences were found within the C2 molecule profile, and it was found that the medium in which C2 molecules reside is denser towards ρ Oph A and ρ Oph B than ρ Oph D. Modelling additional species, such as Fe I and Fe II which are also thought to be present in the data, may help to further characterise the ISM towards these three stars. Optical and near-infrared (IR) observations of Herschel 36 were undertaken using the Southern African Large Telescope (SALT) and Gemini North. The aim of this project was to investigate the full DIB spectrum along this unusual sight-line, and determine how many DIBs were present and how many demonstrate the behaviour previously observed. A number of issues arose with the optical observations and the data reduction processes, meaning that the overall aim was not fully realised. However, observations from Gemini North showed more promise but did not detect either near-IR DIB, although higher S/N observations are recommended to verify their absence.
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O'Neill, Philip Thomas. "Radiative transfer and chemistry in spheroidal interstellar clouds." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252417.
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Beletsky, Yuri. "Extragalactic molecular clouds and chemistry of diffuse interstellar clouds." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-105670.
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Garrod, R. T. "The chemistry of transient dense cores in interstellar clouds." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1446233/.
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I model the chemical effects on dark clouds of their being composed of small (<0.1 pc), transient (order of 1 Myr), dense cores (which are only observed with high-resolution interferometry) within which most of the clouds' mass resides, surrounded by a diffuse background gas. I investigate the chemical evolution of the cores, and the resultant chemical enhancement of the background gas by cyclical processing through core formation and dissipation. I approximate the MHD mechanism of Falleh Hartquist (2002), by which large transient density inhomogeneities may be produced by slow-mode waves in a cold plasma, into a multi-point 1-D chemical code. Molecular freeze-out onto dust grains and subsequent re-injection into the gas phase are switched on or off according to the attainment of a critical visual extinction at individual points. I explore a grid of parameter space in five physical and chemical variables. Among a number of conclusions, I find firstly that multi-point chemical codes are highly necessary for modelling dark cloud regions, due to the large chemical variation over time and space. I find that the core chemistry is young at all times, in keeping with observations, and that the abundance and spatial extent of several important species is significantly enhanced by the cycling process. Further to this, I construct (non-interacting) assemblies of such cores, producing convolved maps mimicking observational constraints, and present evidence that such collections of transient dense cores may reproduce the morphologies observed in both low- and high-resolution molecular line studies of dark clouds. I further modify the convolution method in a number of ways, using this mapping procedure to test hypotheses derived from the chemical analysis. Hence I obtain observational diagnostics for the determination of physical and chemical conditions in dark clouds.
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Stantcheva, Tatiana. "Application of stochastic approaches to modeling of interstellar chemistry." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1085581872.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xii, 146 p.; also includes graphics (some col.) Includes bibliographical references (p. 141-146). Available online via OhioLINK's ETD Center
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Pei, Yezhe. "Application of Stochastic and Deterministic Approaches to Modeling Interstellar Chemistry." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1345216353.
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Hammonds, Mark. "On the chemistry and spectroscopy of PAHs in circumstellar and interstellar environments." Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602526.
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August, J. "Spectroscopic studies of nitriles, enimines and ynamines of importance in interstellar chemistry." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372699.
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Cordiner, Martin. "Diffuse interstellar bands and the structure of the ISM." Thesis, University of Nottingham, 2005. http://eprints.nottingham.ac.uk/11952/.
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This may be interpreted as evidence that the profile of sub-structure of the lambda 6614 DIB is skewed towards the red in these three sightlines (Sk -68°135, Sk -69°223 and Sk -69°243) to a greater degree than that found in the Galactic ISM. Compared to Galactic trends, the LMC DIBs are found to be weak with respect to the reddening and neutral potassium column density towards Sk -67°2 and Sk -68°135. This may be attributable to a combination of the high UV flux and reduced shielding of interstellar clouds due to the low metallicity of the interstellar gas of the LMC, and results in the destruction of DIB carriers by photodissociation and/or photoionisation. Relative to N(H I) the lambda 6284 DIB observed in four LMC sightlines is shown to be approximately 1/5 to 1/2 of its average strength in the Milky Way. This supports the idea that the metallicity and/or dust-to-gas ratio of the ISM is closely linked with the chemistry that governs the abundance of DIB carriers relative to N(H I). Variations in the N(Ca II)/N(Ti II) ratio are found over at least an order of magnitude in the LMC ISM, and are taken as evidence for significant variation in the Ca n/Ca m ionisation balance. Derived logarithmic titanium depletions are found to be relatively low in the six LMC sightlines studied, with values between approximately -0.8 and -1.9, which are similar to the levels of depletion generally seen in the warm, shocked interstellar medium of the Galaxy.
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Blanksby, Stephen J. ""Gas phase synthesis of interstellar cumulenes : mass spectrometric and theoretical studies" /." Title page, contents and summary only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phb6423.pdf.
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Thesis (Ph.D.)-- University of Adelaide, Dept. of Chemistry, 1999.Copies of author's previously published articles inserted. Supplement entitled: Addressing referee concerns, stapled to back end paper (5 leaves). Bibliography: leaves 199-212.
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Tenenbaum, Emily Dale. "MILLIMETER WAVE STUDIES OF CIRCUMSTELLAR CHEMISTRY." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/194941.
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Millimeter wave studies of molecules in circumstellar envelopes and a planetary nebula have been conducted. Using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO) on Mt. Graham, a comparative spectral survey from 215-285 GHz was carried out of the carbon-rich asymptotic giant branch star IRC +10216 and the oxygen-rich supergiant VY Canis Majoris. A total of 858 emission lines were observed in both objects, arising from 40 different molecules. In VY Canis Majoris, AlO, AlOH, and PO were detected for the first time in interstellar space. In IRC +10216, PH3 was detected for the first time beyond the solar system, and C3O, and CH2NH were found for the first time in a circumstellar envelope. Additionally, in the evolved planetary nebula, the Helix, H2CO, C2H, and cyclic-C3H2 were observed using the SMT and the Kitt Peak 12 m telescopes. The presence of these three molecules in the Helix suggests that relatively complex chemistry occurs in planetary nebulae, despite the harsh ultraviolet field. Overall, the research on molecules in circumstellar and planetary nebulae furthers our understanding of the nature of the material that is fed back into the interstellar medium from evolved stars. Besides telescope work, laboratory research was also conducted - the rotational spectrum of ZnCl was measured and its bond length and rotational constants were determined. Lastly, in partial fulfillment of a graduate certificate in entrepreneurial chemistry, the commercial applications of terahertz spectroscopy were explored through literature research.
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Vazart, Fanny. "Gas-phase formation of Complex Organic Models molecules in interstellar medium: computational investigations." Doctoral thesis, Scuola Normale Superiore, 2017. http://hdl.handle.net/11384/85813.
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[excerpt form the abstract:] In the field of astro- and prebiotic chemistry, the building blocks of life, which are molecules composed of more than 6 atoms, are called Complex Organic Molecules (COMs). Their appearances on the early inorganic Earth is therefore one of the major issues faced by researchers interested in the origin of life. In this thesis, split into three parts, the main purpose is to show how different COMs are formed in interstellar medium (ISM), using computational chemistry.
The first part focuses mainly on preliminary studies aiming at evaluating the appropriate level of theory to use to perform studies of formation reactions. First, a comprehensive benchmark of C≡N stretching vibrations computed at harmonic and anharmonic levels is reported with the goal of proposing and validating a reliable computational strategy to get accurate results for this puzzling vibrational mode, involved in biological molcules, without any ad hoc scaling factor.
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Valdivia, Valeska. "Impact of radiative transfer and chemistry on the formation of molecular clouds." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066709/document.
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Le milieu interstellaire (MIS) est un système extrêmement complexe. Il correspond à une échelle intermédiaire entre les étoiles et les galaxies. Le gaz interstellaire est présent dans toute la galaxie, remplissant l’espace entre les étoiles. Une grande diversité de processus couplés, comme la gravité, le champs magnétiques, la turbulence et la chimie, participe à son évolution, faisant de la modélisation du MIS un problème ardu. Une description correcte du MIS nécessite un bon traitement des équations de la magnetohydrodynamique (MHD), de la gravité, du bilan thermique et de l’évolution chimique à l’intérieur du nuage moléculaire.L’objectif de ce travail de thèse est une meilleure compréhension de la formation et de l’évolution des nuages moléculaires, et plus particulièrement de la transition du gaz atomique en gaz moléculaire. Nous avons réalisé des simulations numériques de la formation des nuages moléculaires et de la formation de l’hydrogène moléculaire sous l’influence de la gravité et de la turbulence MHD, en utilisant des estimations précises de l’écrantage par les poussières et de l’auto-écrantage par la molécule H2. Ceci a été calculé grâce à une méthode en arbre, à même de fournir une rapide estimation des densités de colonne.Nous avons trouvé que l’hydrogène moléculaire se forme plus rapidement que prévu par les estimations classiques du fait de l’augmentation de densité locale provoquée par les fluctuations turbulentes du gaz. L’hydrogène moléculaire, formé à des densités plus élevées, peut alors migrer vers les régions plus chaudes et moins denses.Les densités de colonne totale d’hydrogène moléculaire montrent que la transition HI-H2 se produit à des densités de colonne de quelques 10^20 cm−2. Nous avons calculé les populations des niveaux rotationnels de H2 à l’équilibre thermique et intégré le long de plusieurs lignes de visée. Ces résultats reproduisent bien les valeurs observées par Copernicus et FUSE, suggérant que la transition observée et les populations excitées pourraient être une conséquence de la structure multi-phasique des nuages moléculaires. Comme la formation de H2 précède la formation des autres molécules, le H2 chaud pourrait permettre le développement d’espèces endothermiques et éventuellement expliquer certains aspects de la richesse moléculaire observée dans l’ISMThe interstellar medium (ISM) is a highly complex system. It corresponds to an intermediate scale between stars and galaxies. The interstellar gas is present throughout the galaxy, filling the volume between stars. A wide variety of coupled processes, such as gravity, magnetic fields, turbulence and chemistry, participate in its evolution, making the modeling of the ISM a challenging problem. A correct description of the ISM requires a good treatment of the magnetohydrodynamics (MHD) equations, gravity, thermal balance, and chemical evolution within the molecular clouds.This thesis work aims at a better understanding of the formation and evolution of molecular clouds, specially how they become "molecular", paying particular attention to the transition HI-to-H2. We have performed ideal MHD simulations of the formation of molecular clouds and the formation of molecular hydrogen under the influence of gravity and turbulence, using accurate estimates for the shielding effects from dust and the self-shielding for H2, calculated with a Tree-based method, able to provide fast estimates of column densities.We find that H2 is formed faster than predicted by the usual estimates due to local density enhancements created by the gas turbulent motions. Molecular hydrogen, formed at higher densities, could then migrate toward low density warmer regions.Total H2 column densities show that the HI-to-H2 transition occurs at total column densities of a few 10^20 cm−2. We have calculated the populations of rotational levels of H2 at thermal equilibrium, and integrated along several lines of sight. These two results reproduce quite well the values observed by Copernicus and FUSE, suggesting that the observed transition and the excited populations could arise as a consequence of the multi-phase structure of molecular clouds. As H2 formation is prior to further molecule formation, warm H2 could possibly allow the development of a warm chemistry, and eventually explain some aspects of the molecular richness observed in the ISM
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Edwards, Samuel Joseph. "Experimental Studies of Ion-Neutral Chemistry Related to the Extraterrestrial Environment." Thesis, University of Canterbury. Chemistry, 2009. http://hdl.handle.net/10092/2224.
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Kinetic data is presented for a variety of ion-neutral reactions which are relevant to the atmosphere of Titan and to the chemistry occurring in interstellar clouds. The data were recorded with a Selected Ion Flow Tube (SIFT) operating at room temperature (294 ± 4 K) and at a pressure of 0.46 Torr. Results of the recent Cassini-Huygens mission to Saturn and Titan have identified several species in the atmosphere of Titan not predicted by pre-Cassini models of the atmosphere. In order to determine the fate of three of these species (methylenimine, propionitrile and cyanodiacetylene) in Titan's ionosphere, their reactivity with the principal ions in Titan's upper ionosphere has been examined. As expected, collision rate proton transfer reactions dominate the chemistry with association channels also observed with many of the hydrocarbon ions. The results of the Cassini mission also identified several individual reactions as being of potential importance to models of Titan's atmosphere and this chemistry has also been examined. The above studies are also relevant to the interstellar medium where each of the neutral reactants have also been detected. The results of some proton transfer equilibrium studies are also presented. The gas phase basicities of propyne and acetylene have been determined to be 681 kJ mol⁻¹ and 617.4 kJ mol⁻¹ respectively. Their relative proton affinities can be estimated from these values. A combined experimental/theoretical study of the proton affinity of cyanodiacetylene (HC₅N) has enabled this value to be estimated at 770 ± 20 kJ mol⁻¹. Details of an attempt to complete the first laboratory measurement of the crucial reaction between H₃⁺ and atomic carbon are presented. The generation of atomic carbon in sufficient quantities for reaction in the SIFT was not possible with the microwave discharge source used. Other generation methods have also been explored with the laser photolysis of carbon suboxide expected to provide a possible solution to the problems encountered. The results of an investigation into the applicability of lithium ions (Li⁺) to SIFT-MS are presented. The lithium ions associated with each of the twenty-one neutral analytes examined to form pseudo-molecular ions. The association reactions were rapid (k ~ 10⁻⁹ cm³ s⁻¹) for large hydrocarbons but were much slower for smaller analytes (k < 10⁻¹¹ cm³ s⁻¹). In order to clarify some unusual experimental observations, the effect of water molecules on the observed chemistry has been examined in detail. The measured chemistry has important consequences for the applicability of Li⁺ to SIFT-MS where the presence and detection of an identifiable ion of the analyte is essential. Details of new SIFT operating software which can be run on a modern computer are given. Mass spectra and kinetic data recorded with the new software are also presented.
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Pulliam, Robin L. "Observational and Experimental Astrochemistry: A High Resolution Gas Phase Study of Metal Containing Species in the Laboratory and Circumstellar Envelopes of Stars." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/222611.
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It was once thought that molecules in the interstellar medium (ISM) would be destroyed in the harsh surroundings and conditions of space, and therefore unobservable by radio techniques. However, it is now understood that the chemistry of the ISM is vast and complex. The question still remains as to just how complex is this chemistry. Much is clearly still not understood. This dissertation presents work on the study of metal compounds and cations in the circumstellar envelopes of oxygen- and carbon-rich asymptotic giant branch (AGB) and supergiant stars. Laboratory studies were also conducted on several transition metal compounds of interstellar interest, some with high spin and orbital angular momentum states. Work has been completed to confirm the detection of the debated metal cyanide KCN in the carbon-rich AGB star IRC+10216. KCN joins the list as the fifth interstellar metal cyanide/isocyanide detected in this source. In addition, preliminary results on the search for TiO are presented towards the oxygen-rich supergiant star, VY CMa. To further understand the evolutionary processes of carbon- and oxygen-rich stars, a survey of HCO⁺ was taken towards the carbon star IRC+10216, the oxygen-rich AGBs TX Cam, IK Tau, and W Hya and the oxygen-rich supergiant NML Cyg. While HCO⁺ was detected towards all of these sources, the results vary. The outflow of NML Cyg proves to be asymmetric and further study is necessary. The emission from W Hya is significantly narrower than the other sources. The abundances of HCO⁺ in circumstellar gas increases inversely with mass-loss rate and ion-molecule chemistry appears to influence the chemistry of evolved circumstellar envelopes. To understand species in space with more confidence, a laboratory search for several 3d transition metal species of astrochemical interest was conducted in the laboratory: HZnCl (X¹∑⁺), ZnO (X¹∑⁺ and a³Πᵢ), ZnCl (X²∑⁺), TiS (X³Δᵣ) and CrS (X⁵Πᵣ). All of the molecules have been observed for the first time with high resolution gas phase rotational spectroscopy and the work on ZnO was the first gas-phase study of this molecule. Synthesis of the species required exotic production methods, including use of a DC discharge to produce all zinc species. By studying the rotational spectra, rest frequencies were determined that will be beneficial for future astronomical searches.
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Vásquez, Mencos Abraham Alejandro. "The Nitrogen Chemistry in Solid Phase at Cryogenic Temperatures : Molecular Evolutions in Interstellar Clouds and Planetary Atmospheres." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS256.
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L'azote est le cinquième élément le plus abondant de l'Univers, et les réservoirs les plus importants de cet élément sont les nuages moléculaires et les disques proto-planétaires. En raison des conditions du milieu interstellaire, la majeure partie de l'azote existe sous forme atomique. Bien que les espèces azotées soient très abondantes dans le milieu interstellaire et dans certaines atmosphères planétaires et cométaires, peu d’études de laboratoire ont été réalisées visant à comprendre le rôle d'azote atomique dans la chimie de ces régions de l'Univers. Dans cette thèse, nous avons exploré la réactivité, en phase solide et aux températures cryogéniques, de l'azote atomique à l’état fondamental N(4S) avec des composés organiques simple comme CH4 et CH3CN. Les réactifs, produits et intermédiaires de réaction sont sondés in situ par spectroscopie infrarouge à transformée de Fourier (IRTF). Nous avons montré, dans une première étape, que le chauffage progressif de nos échantillons solides entre 3 et 10 K, stimule la recombinaison atomique N(4S) - N(4S) et la formation de formes excités de l'azote atomique et moléculaire, N2(A) et N(2D). Ces espèces sont très réactives et jouent un rôle essentiel dans la dissociation de composés organiques. Dans une seconde étape, le chauffage continu de 10 à 40 K induit principalement des recombinaisons des radicaux formés dans la première étape conduisant à la formation de molécules organiques complexes comme NH3, C2H6, HCN et HNC. Ces travaux de recherche décrivent le rôle de l'azote atomique en phase solide des nuages moléculaires comme étant très semblable à celui des rayonnements UV dans les nuages diffusNitrogen is the fifth most abundant element in the Universe, and the most significant reservoirs of this element are molecular clouds, dark clouds, and proto-planetary discs. Due to the conditions of the interstellar medium, most of the nitrogen exists in atomic form. Even the enormous abundance of this element there are not many studies aimed at understanding the role that nitrogen plays in the chemistry of dark molecular clouds and other cold regions of the Universe where the UV light and other energetic particles are not able to penetrate. In the present Ph-D thesis, we have explored the reactivity of atomic nitrogen in ground state N(4S) thermally induced with small organic compounds in the solid phase at cryogenic temperatures from 3 to 40K using Fourier Transform Infrared Spectroscopy (FTIR) analysis. We have shown that gradual heating in a first step, between 3 and 10K, stimulates N(4S) - N(4S) recombination and the consequent formation of the excited forms of nitrogen N2(A) and N(2D). These species play an essential role in the dissociation of H-C bearing species to form radicals. Then, in a second step, the continuous heating from 10 to 40K, induces the recombination of the radicals formed in the first step to produce more stable and complex compounds. During this process, there are observed reactions of addition, H-elimination, C-N, C-C formation, molecular fragmentation and isomerization. From these experiments, we have demonstrated that role of atomic nitrogen in dark molecular clouds is equivalent to that of UV light in diffuse clouds
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Peppe, Salvatore. "Some unusual, astronomically significant organic molecules." Title page, contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09PH/09php4241.pdf.
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Appendix inside back cover. "June 2002" Bibliography: leaves 157-168. Experimental and theoretical studies were carried out on a number of unusual organic molecules of potential astronomical significance. The experimental work was corroborated by various theoretical approaches and by utilising computer-based quantum chemical calculations. Various covalently bound, anionic and neutral oxocarbon species were formed and studied. Additionally, two analogous heterocumulenic systems were investigated. Some isomers of either system, when energised, were shown to undergo gas-phase rearrangement processes.
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Ouellette, Mélanie. "Gas-phase Ion Chemistry of Hydroxy and Amino-substituted Interstellar Polycyclic Aromatic Hydrocarbons and Protonated Polycyclic Aromatic Hydrocarbons." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31349.
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The gas-phase ion chemistry of hydroxyl- and amino-substituted polycyclic aromatic hydrocarbons (PAHs) and their protonated counterparts were studied using mass spectrometry. Ions were generated using an electron ionization (EI) source and the unimolecular chemistry of metastable ions was studied by performing mass-analysed ion kinetic energy spectrometry (MIKES) experiments with a magnetic sector tandem mass spectrometer. Collision-induced dissociation (CID) experiments were used in conjunction with MIKES experiments to determine ion structure. The ten molecules studied were: 1-naphthol, 2-naphthol, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 1-phenanthrol, 9-phenanthrol, 1-hydroxypyrene and 1-aminopyrene. Since it is believed that larger PAHs, on the order of more than 50 carbon atoms, populate the interstellar medium, the goal of this study was to attempt to extrapolate the results from smaller systems to larger ones. The trends found include: hydroxy-substituted PAH radical cations lose carbon monoxide spontaneously and amino-substituted PAH radical cations lose HCN. Mechanisms for both processes are proposed, and it appears from the present results that this process should extrapolate to larger PAHs. Another trend found was that all the remaining fragment ions were always a closed ring. Protonated amino-substituted PAHs were generated by electrospray ionization using a quadruple time-of-flight mass spectrometer. By protonating 1-naphthol and 2-naphthol using methane in the high-pressure EI source, it was found that they lost exclusively H2O. As for 2-naphthylamine, 1-aminoanthracene and 2-aminoanthracene, it was found that 2-naphthylamine lost NH3 and a hydrogen atom, NH3being the dominant channel. However, as the ion size 3 increases, the hydrogen-loss channel became the dominant channel. This means that larger PAHs will likely lose exclusively a hydrogen atom to reform the parent radical cation.
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Sheehan, Clinton H. "A merged beam analysis of the dissociative recombination of molecular ions of importance to ionospheric and interstellar chemistry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ58189.pdf.
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Jamal, Eddine Nour. "Reactivity of molecular anions at low temperature : implications for the chemistry of the interstellar medium ant Titan's atmosphere." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S132/document.
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Depuis leur découverte dans divers environnements astrophysiques, les anions polyyne CxH¯ (x = 2, 4, 6) et les anions cyanopolyyne CxN¯ (x = 1, 3, 5) ont reçu une attention considérable. Ces anions semblent jouer des rôles importants dans leur environnement. Cependant, les données à basse température sur les voies chimiques menant à leur formation et à leur destruction sont encore rares, en particulier ce qui concerne l'identité du produit et les ratios de ramification. Pour résoudre ce problème, nous nous sommes engagés dans la recherche de la réactivité de ces anions moléculaires en utilisant des instruments dédiés couplant des jets subsonique et supersonique avec des méthodes de spectrométrie de masse. De cette façon, nous avons étudié la réactivité des anions C3N avec le cyanoacétylène (HC3N) ainsi que la réactivité de CN¯, C3N¯, et C5N¯ avec l'acide formique (HCOOH) de 298 K à des températures aussi basses que 36 K. Nous rapportons dans ce travail le taux de vitesse, les produits, et les ratios de ramification de ces réactions. Ce travail aborde également la source prototype d'ions sélectionnée, qui a récemment été mis en place dans notre laboratoire afin d'étendre notre recherche à d'autres anions d'intérêt astrophysique (e.g. les anions CxH¯ et Cx¯). Une description de cet instrument ainsi que des résultats préliminaires sont présentés dans ce travail. Cette thèse, «Reactivity of Molecular Anions at Low Temperature: Implications for the Chemistry of the Interstellar medium and Titan’s atmosphere», a été réalisée au sein de l'Institut de physique de Rennes et de l'Ecole Nationale Supérieure de Chimie de Rennes. Mots-clés: astrochimie, atmosphère de Titan, anions moléculaires, cinétique en phase gazeuse, jet supersonique, spectrométrie de masse, source d’ions sélectionnéeEver since their discovery in various astrophysical environments, polyyne anions CxH¯ (x = 2, 4, 6) and cyanopolyyne anions CxN¯ (x = 1, 3, 5) have received a considerable attention. These anions appear to be playing important roles in their environments. However, low temperature data on the chemical pathways leading to their formation and destruction is still scarce, especially regarding product identity and branching ratios. To address this issue, we have engaged in the investigation of the reactivity of these molecular anions by employing dedicated instruments coupling subsonic and supersonic flows with mass spectrometry methods. In this fashion, we have investigated the reactivity of C3N¯ anions with cyanoacetylene (HC3N) as well as the reactivity of CN¯, C3N¯, and C5N¯ with formic acid (HCOOH) from 298 K down to temperatures as low as 36 K. We report in this work the rate coefficient, the nature of the products, and the branching ratios of these reactions.This work also addresses the prototype selected ion source in our laboratory, which was recently implemented in order to extend our investigation to other anions of astrophysical interest (e.g. CxH¯ and Cx¯ anions). A description of this instrument as well as some preliminary results are presented in this work. This thesis, «Reactivity of Molecular Anions at Low Temperature: Implications for the Chemistry of the Interstellar medium and Titan’s atmosphere», was carried out at the Institut de Physique de Rennes and the Ecole Nationale Supérieure de Chimie de Rennes.Keywords: astrochemistry, Titan’s atmosphere, molecular anions, gas phase kinetics, supersonic flow, mass spectrometry, selected ion source
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Dawley, Margaret Michele. "Radiation and thermal processing of ices and surfaces relevant to prebiotic chemistry in the solar system and interstellar regions." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51767.
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This dissertation has investigated the adsorption, thermal behavior, and radiation (both photon and electron) processing of prebiotically-relevant ices and surfaces. A custom ultra-high vacuum (UHV) chamber has been built that is coupled with a Fourier Transform-Infrared (FT IR) spectrometer and a Temperature Programmed Desorption (TPD) system that utilizes Quadrupole Mass Spectrometry (QMS) to study selected organic:surface systems. Formamide (HCONH₂) has been studied in two related but distinct studies relevant to primitive Earth and interstellar chemistry. First, in collaboration with a theory group, formamide’s interaction with kaolinite (Al6Si6O36H30), a clay mineral relevant to early Earth chemistry, has been studied experimentally and theoretically. Experimental infrared results are compared with calculated infrared frequencies obtained by our collaborators. TPD analysis is compared with the calculated values of adsorption energy, and the optimal kaolinite termination site for adsorption is reported. Second, the first thermal and radiation damage study of pure formamide and HCONH₂:H₂O mixed ices on an interstellar icy grain analog (SiO₂) is reported. A discussion of the pure formamide ice phases identified with FT-IR upon warm-up, as well as the TPD binding energies of HCONH₂ on SiO₂, is presented. The observed Lyman-alpha photochemical products and proposed formation mechanisms from pure formamide ice is reported and discussed. In addition, results of Lyman alpha processing of mixed HCONH₂:H₂O ices are provided. Low-energy electron irradiation of pure HCONH₂ and HCONH₂:H₂O mixed ices has also been reported for the first time. A third investigation has studied acetylene (C₂D₂) and acetonitrile (CH₃CN) interactions and radiation stability in mixed low-temperature ices to simulate possible prebiotic reactions that may occur on Saturn’s moon, Titan. This investigation contributes to understanding the possible consumption, trapping, and degradation of these species on the surface of Titan.
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Zicler, Eléonore. "Chimie quantique et cosmologie : de la recherche de l'hélium moléculaire à la variation de la constante de structure fine." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066558/document.
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L’hélium, deuxième élément le plus abondant de l’univers après l’hydrogène (He/H ~ 1/10), n’a étonnamment jamais été observé sous une autre forme que celle d'atomes neutres ou ionisés dans le milieu interstellaire (MIS). L’hélium étant un gaz noble peu réactif, sa non-observation au sein d’un édifice moléculaire neutre est compréhensible mais cela est plus surprenant pour des espèces chargées positivement comme HeH+, [HeH3]+ ou CHe2+. La première partie de cette thèse a pour but de proposer des raisons chimiques à cette non-observation à l’aide de calculs de chimie quantique de haut niveau (CASPT2) couplés à des calculs d’association radiative. Au vu des résultats sur les mécanismes de destruction de HeH+, nous suggérons une zone du MIS où il serait envisageable de le détecter.La seconde partie de ce travail porte sur la possibilité de détection de variations temporelles des constantes fondamentales de la physique. En 1999, Webb et al., après analyse de la lumière issue de quasars lointains, affirmèrent que la constante de structure fine α pouvait avoir été plus faible par le passé. Aucune étude postérieure ne vint confirmer ce résultat. Il était donc important de déterminer théoriquement dans quelle mesure une telle variation affecterait le spectre électronique de petites molécules primordiales afin d’en évaluer la détectabilité par les instruments actuels. Nous avons pour cela mis au point un protocole ab initio qui évalue le décalage spectral induit par une variation d’α. Les calculs (niveau MRCI) montrent qu’une variation d’α de l’ordre de grandeur de ce que Webb et al. auraient détecté induirait des déplacements de raies non décelables par les télescopes actuelsDespite Helium is the second most abundant element in the Universe (He/H ~ 1/10), it has never been observed in any other forms than that of an atom or an ion in the InterStellar Medium (ISM). Since He is a noble gas, its non-observation as part of neutral molecular systems is understandable, but it is quite surprising for positively charged species like HeH+, [HeH3]+ or CHe2+. The first part of this study aims at finding a chemical reason for such a non-observation and in particular for the three ions mentioned above. For that purpose, we have computed high level quality (CASPT2) energy hyper-surfaces and performed radiative association calculations. Finally, we are able to suggest a region of the ISM where the detection of HeH+ might be achieved.The second part of this work deals with the possibility that the fundamental constants could be time-dependent. In 1999, Webb et al., analyzing the quasar emissions, claimed that the fine structure constant α could have been smaller in the past, but this result has not been confirmed. Thus it seemed necessary to determine theoretically how much such a variation could affect the electronic spectra of some primordial molecules in order to determine whether such variations might be detectable or not with the current observational instrumentation. For that purpose, we have developed an ab initio protocol to evaluate the shift induced by a variation of α. High level quantum chemistry calculations (MRCI) show that a variation of α of the same order of magnitude than that reported by Webb et al., would induce shifts that are not detectable by the current telescopes
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Adande, Gilles Rapotchombo. "Microwave and Millimeter Wave Astrochemistry: Laboratory Studies of Transition Metal-Containing Free Radicals and Spectroscopic Observations of Molecular Interstellar Environments." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/306775.
Full textAbstract:
Progress in our understanding of the chemical composition of the interstellar medium leans both on laboratory analyses of high resolution rotational spectra from molecules that may be present in these regions, and on radio astronomical observations of molecular tracers to constrain astrochemical models. Due to the thermodynamic conditions in outer space, some molecules likely to be found in interstellar regions in relevant abundances are open shell radicals. In a series of laboratory studies, the pure rotational spectra of the transition metal containing radicals sulfur species ScS, YS, VS and ZnSH were obtained for the first time. In addition to accurate and precise rest frequencies for these species, bonding characteristics were determined from fine and hyperfine molecular parameters. It was found that these sulfides have a higher degree of covalent bonding than their mostly ionic oxide counterparts. Isomers and isotope ratios are excellent diagnostic tools for a variety of astrochemical models. From radio observations of isotopes of nitrile species, the galactic gradient of ¹⁴N/¹⁵N was accurately established. A further study of this ratio in carbon rich asymptotic giant branch stars provided observational evidence for an unknown process in J type carbon stars, and highlighted the need to update stellar nucleosynthesis models. Proper radiative transfer modeling of the emission spectra of interstellar molecules can yield a wealth of information about the abundance and distribution of these species within the observed sources. To model the asymmetric emission of SO and SO₂ in oxygen-rich supergiants, an in-house code was developed, and successfully applied to gain insight into circumstellar sulfur chemistry of VY Canis Majoris. It was concluded that current astrochemistry kinetic models, based on spherical symmetry assumptions, need to be revisited.
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Ruaud, Maxime. "Chimie du milieu interstellaire : du diffus au dense." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0099/document.
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L’évolution chimique des phases les plus diffuses aux plus denses du milieu interstellaireest un processus continu : la composition chimique du milieu interstellairedans une phase dépend de sa composition dans sa phase antérieure.Les études, qui s’intéressent à la chimie du milieu dense et froid ainsi qu’à l’évolutionde sa composition au cours du temps, font de fortes hypothèses sur son évolutiondepuis le milieu diffus.L’objectif de ma thèse a donc été de suivre l’évolution de la chimie de la matièreinterstellaire du milieu diffus jusqu’à la formation des nuages denses.J’ai pour cela utilisé un modèle de chimie gaz-grain dépendant du temps que j’aisignificativement contribué à améliorer pour la partie chimie de surface. J’ai dansun premier temps suivi une approche "classique" (c.-à-d. : semblable aux études préexistantes)de la modélisation des régions froides. Cela m’a permis d’étudier en détailles processus physiques et chimiques à l’origine de la complexité moléculaire dans lesnuages denses et froids et de comparer les prédictions du modèle avec les études existantes.Dans une deuxième partie, j’ai appliqué ce modèle pour suivre l’évolution de lacomposition chimique du milieu interstellaire au cours du processus de formation desnuages moléculaires à partir du milieu diffus. Pour cette étude, j’ai utilisé les résultatsd’une simulation hydrodynamique à l’échelle galactique. Cela m’a permis de montrerque l’histoire de l’évolution des conditions physiques dans les phases antérieures à laformation des nuages moléculaires peut avoir un impact significatif sur la compositionchimique de ces derniersThe chemical evolution from the most diffuse parts of the interstellar medium tothe formation of dense clouds is a continuous process : the chemical composition inone phase depends on the chemical composition in the previous one.However, most studies of the time dependent chemistry in the cold and dense interstellarmedium make strong assumptions on the transition between diffuse and densemedium.The goal of my thesis was to study the chemical evolution of the interstellar mediumfrom the most diffuse parts to the formation of dense clouds in a continuousway.To do so, I used a time dependent gas-grain model that I significantly contributedto improve for the treatment of the surface chemistry. In a first part, I followed a "classical"approach (i.e. : similar to most of the pre-existing studies) to model cold denseclouds. This allowed me to study in details the physical and the chemical mechanismsresponsible for the chemical complexity of dense clouds and to compare the modelpredictions with the existing literature. In a second part, I applied this model to followthe evolution of the chemical composition during the formation process of denseclouds from the diffuse medium. I used results from an hydrodynamical simulation ofthe interstellar medium at galactic scales. This study allowed me to show that the pastphysical history of each particles that form the dense clouds have a significant impacton their chemical composition
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Pearcy, Adam C. "Non-covalent and covalent interactions between phenylacetylene and quinoline radical cations with polar and non-polar molecules in the gas phase." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5990.
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Gas phase molecular clusters present an ideal medium for observing factors that drive chemical reactions without outside interferences from excessive solvent molecules. Introducing an ion into the cluster promotes ion-molecule interactions that may manifest in a variety of non-covalent or even covalent binding motifs and are of significant importance in many fields including atmospheric and astronomical sciences. For instance, in outer space, molecules are subject to ionizing radiation where ion-molecule reactions become increasingly competitive to molecule-molecule interactions. To elucidate individual ion-molecule interaction information, mass spectrometry was used in conjunction with appropriate theoretical calculations.
Three main categories of experiment were conducted in this dissertation. The first of which were thermochemical equilibrium measurements where an ion was introduced to an ion mobility drift cell wherein thermalizing collisions occur with helium buffer gas facilitating a reversible reaction with a neutral molecule allowing the standard changes in enthalpy and entropy to be determined. The second type of experiment was an ion mobility experiment where an ionized homo- or hetero-cluster was injected into the drift cell at specific conditions allowing the reduced mobility and collisional cross-section to be evaluated. Thirdly, kinetics measurements were taken following injection of an ion into the drift cell were an irreversible reaction ensued with the neutral species hindering equilibrium, but prompting rate constant assessment.
Previous research has laid the groundwork for this dissertation as the results and discussion contained herein will build upon existing data while maintaining originality. For example, past work has given support for ion-molecule reactions involving precursor species such as acetylene and hydrogen cyanide to form more complex organics, perhaps leading to biologically relevant species. The chemical systems studied for this research are either ionized substituted benzenes like phenylacetylene and benzonitrile or polycyclic aromatic nitrogen-containing hydrocarbons like quinoline and quinoxaline interacting with a variety of neutral species.
Hydrogen bonding and its many sub-sections are of the utmost importance to the kinds of reactions studied here. Past work has shown the tendency of organic radical cations to form conventional and unconventional ionic hydrogen bonds with gas phase solvents. Other non-covalent modes of interaction have also been detected in addition to the formation of covalently bound species. Gas phase reactions studied here will explore, via mass-selected ion mobility, reversible and irreversible reactions leading to binding enthalpy and entropy and rate constant determination, respectively, in addition to collisional cross-section determination.
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Fortenberry, Ryan Clifton. "Theoretical Prediction of Electronically Excited States and Vibrational Frequencies of Interstellar and Planetary Radicals, Anions, and Cations." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/26329.
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In the search for molecular species in the interstellar medium and extraterrestrial planetary atmospheres, theoretical methods continue to be an invaluable tool to astronomically minded chemists. Using state-of-the art methods, this doctoral work characterizes the electronically excited states of interstellar radicals, cations, and even rare anions and also predicts the gas phase fundamental vibrational frequencies of the cis and trans-HOCO radicals, as well as the cis-HOCO anion. First, open-shell coupled cluster methods of singles and doubles (CCSD) and singles and doubles with triples-inclusion (CC3) are tested on the C2H and C4H radicals. The significant double-excitation character, as well as the quartet multiplicity of some states yields inaccurate excitation energies and large spin contamination with CCSD. CC3 somewhat improves this for select states, but discrepancies between CC and multiref- erence results for certain states exist and likely arise from the lack of spin adaptation in conventional spin-orbital CC. Next, coupled-cluster methods predict the presence of an ex- cited state of the closed-shell allyl cation and its related H2CCCHCH2+ cousin at 443 nm near an unidentified laboratory peak at 442.9 nm which is also close to one of the largest unattributed interstellar absorption features. Additionally, the dipole moments, electron binding energies, and excited states of neutral radicals and corresponding closed-shell anions of interstellar interest are also computed. These are calibrated against experimental data for CH2CNâ and CH2CHOâ . Since coupled cluster theory closely reproduces the known experimental data, dipole-bound excited states for eight previously unknown anions are pre- dicted: CH2SiNâ , SiH2CNâ , CH2SiHOâ , SiNâ , CCOHâ , HCCOâ , SiCCNâ , and SiNCâ . In addition, we predict the existence of one rare valence-bound excited state of CH2SiNâ and
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also SiCCNâ as well as even rarer two valence-bound states of CCSiNâ . Lastly, the reaction of CO + OH and its transient potential intermediate, the HOCO radical, may be responsible for the regeneration of CO2 in the Martian atmosphere, but past spectroscopic observations have not produced a full gas-phase set of the fundamental vibrational frequencies of the HOCO radical. Using established, highly-accurate quantum chemical coupled cluster tech- niques and quartic force fields, all six fundamental vibrational frequencies for 1 2Aâ ² cis and trans-HOCO and 1 1Aâ ² cis-HOCOâ are computed in the gas phase.Ph. D.
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Petrie, Simon Antony Hudson. "A selected-ion flow tube study of some gas-phase ion-molecule reactions of potential relevance to the chemistry of dense interstellar clouds." Thesis, University of Canterbury. Chemistry, 1991. http://hdl.handle.net/10092/7253.
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Results are reported for the studies of several systems of ion-molecule reactions of potential relevance to the chemistry of interstellar clouds. Measurements were obtained using a selected-ion flow tube operated at room temperature (300 ± 5 K) and using helium buffer gas at a pressure of 0.30 ± 0.01 Torr.
The proton affinities of C₄H₂ and C₂N₂ were determined by measurement of the rate coefficients for forward and reverse proton transfer reactions involving compounds of similar proton affinity. The results obtained were P A(C₂N₂) = 674 ± 4 kJ mol-¹ and PA(C₄H₂) = 741 ± 4 kJ mol-¹: this latter quantity is significantly below the literature value, based on an earlier measurement obtained from ICR bracketing.
Isomerism of the ions C₂N⁺, C₃N⁺, CHN⁺ and CH₂N⁺ was investigated, using reactivity with various neutrals to distinguish between isomers. The ions CCN⁺/CNC⁺ and CCCN⁺/c-C₃N⁺ were distinguished on the basis of their reactivity with H₂: in both instances, the isomer featuring a terminal N atom reacted rapidly while the other isomer was unreactive. Identification of the isomers HCN⁺/HNC⁺ was complicated by the occurrence of tautomerisation of HCN⁺ to the more stable isomer HNC⁺ by the mechanism of 'forth and back' proton transfer which occurred with several neutral reagents: reaction with CF₄ was subsequently used to distinguish between these isomers, since HCN⁺ reacted rapidly with CF₄ while HNC⁺ was unreactive. The reactions of all of these isomeric systems were examined with several neutrals abundant in interstellar clouds. The ions HCNH⁺ and CNH₂⁺ could not be distinguished on the basis of reactivity with the neutrals surveyed: we cannot exclude the possibility that only one of these isomers, HCNH⁺, was formed using the ion producing methods used.
The reactivity of several ions C₃HnN⁺ (n = 1 → 4) and C₃HnO⁺ (n = 0 → 3), with various neutrals, was investigated to ascertain the importance of these ions in the interstellar synthesis of acrylonitrile, tricarbon monoxide and propynal. Several ion-molecule reactions of CH₂CHCN were also studied to this end. The results indicate that C₃HnN⁺ (n > 0) and C₃HnO⁺ (n > 0) are unreactive with the most prominent cloud constituents H₂ and CO; thus dissociative recombination of these ions should represent a significant source of the target molecules. Several ion-molecule reactions of the types X⁺ + CH₂HCN, and C₃nN⁺ + X, produce ions which, on dissociative recombination, are expected to yield cyanopolyynes and cyclopropenylidene. Several reactions of the C₃HnO+ ions suggest pathways to higher-order polycarbon monoxides and dioxides.
The reactivity of the molecular ions of C₂N₂, C₄N₂ and C₃0₂ have also been studied, to gauge the likely consequences of reactions of such ions within interstellar clouds.
The thermochemistry of the reaction HCN⁺ + CF4₄ → CF₃⁺ + HF + CN is explored with regard to the proposal that this reaction may be 'entropy-driven'.
The interstellar significance of a novel class of neutral-neutral reactions has been considered.
The reactivity of the ions C₄Hn⁺ (n = 0 → 4), C₃HnN⁺ (n = 0 → 4), and C₃HnO⁺ (n = 0 → 3) with the neutrals H₂, CO, C₂H₂ and HCN is discussed in greater detail.
Previous studies have determined that ions featuring linear carbon-chain skeletons are more reactive with H₂ and with CO if they feature 'bare' (non-hydrogenated) terminal carbon atoms: the present study suggests that ions with bare terminal C atoms are also more reactive than ions where the terminal atom is N or 0 rather than C. This observation may be explained by the degree of carbene character evident in such ions. These results are also discussed with reference to the predominance of very highly unsaturated linear molecules within interstellar clouds.
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Landera, Alexander. "Formation of Polycyclic Aromatic Hydrocarbons and Nitrogen Containing Polcyclic Aromatic Compounds in Titan's Atmosphere, the Interstellar Medium and Combustion." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/991.
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Several different mechanisms leading to the formation of (substituted) naphthalene and azanaphthalenes were examined using theoretical quantum chemical calculations. As a result, a series of novel synthetic routes to Polycyclic Aromatic Hydrocarbons (PAHs) and Nitrogen Containing Polycyclic Aromatic Compounds (N-PACs) have been proposed. On Earth, these aromatic compounds originate from incomplete combustion and are released into our environment, where they are known to be major pollutants, often with carcinogenic properties. In the atmosphere of a Saturn’s moon Titan, these PAH and N-PACs are believed to play a critical role in organic haze formation, as well as acting as chemical precursors to biologically relevant molecules. The theoretical calculations were performed by employing the ab initio G3(MP2,CC)/B3LYP/6-311G** method to effectively probe the Potential Energy Surfaces (PES) relevant to the PAH and N-PAC formation. Following the construction of the PES, Rice-Ramsperger-Kassel-Markus (RRKM) theory was used to evaluate all unimolecular rate constants as a function of collision energy under single-collision conditions. Branching ratios were then evaluated by solving phenomenological rate expressions for the various product concentrations. The most viable pathways to PAH and N-PAC formation were found to be those where the initial attack by the ethynyl (C2H) or cyano (CN) radical toward a unsaturated hydrocarbon molecule led to the formation of an intermediate which could not effectively lose a hydrogen atom. It is not until ring cyclization has occurred, that hydrogen elimination leads to a closed shell product. By quenching the possibility of the initial hydrogen atom elimination, one of the most competitive processes preventing the PAH or N-PAC formation was avoided, and the PAH or N-PAC formation was allowed to proceed. It is concluded that these considerations should be taken into account when attempting to explore any other potential routes towards aromatic compounds in cold environments, such as on Titan or in the interstellar medium.
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Edwards, Jessica Louise. "Chemistry in the Final Stages of Stellar Evolution: Millimeter and Submillimeter Observations of Supergiants and Planetary Nebulae." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/565895.
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High mass loss rates in evolved stars make them the major contributors to recycling processed material back into the interstellar medium. This mass loss creates large circumstellar shells, rich in molecular material. This dissertation presents millimeter and submillimeter studies of the end stages of low mass and high mass stars in order to probe their molecular content in more detail. In low mass stars, the molecular material is carried on into the planetary nebula (PN) stage. Observations of CS, HCO⁺, and CO in planetary nebulae (PNe) of various post-asymptotic giant branch ages have shown that molecular abundances in these objects do not significantly vary with age, as previously thought. More detailed observations of the slightly oxygen-rich PN NGC 6537 resulted in the detection of CN, HCN, HNC, CCH, CS, SO, H₂CO, HCO⁺ and N₂H⁺, as well as numerous ¹³C isotopologues. Observations of the middle-aged PN M2-48 showed the presence of CN, HCN, HNC, CS, SO, SO₂, SiO, HCO⁺, N₂H⁺, and several ¹³C isotopologues. These observations represent the first detections of CS, SO, SO₂, and SiO in any planetary nebula. The implications of these observations are discussed. A 1 mm spectral survey of the supergiant star NML Cygni has been carried out with the Arizona Radio Observatory Submillimeter Telescope resulting in the observation of 102 emission features arising from 17 different molecules and 4 unidentified features. The line profiles observed in this circumstellar shell are asymmetric and vary between different molecules, akin to what has been seen in another supergiant, VY Canis Majoris. The non-LTE radiative transfer code ESCAPADE has been used to model molecular abundances in the various asymmetric outflows of VY Canis Majoris, showing just how chemically and kinematically complex these supergiant circumstellar envelopes really are.
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Yuan, Bing. "Variable Temperature Rate Coefficient Studies through a Coaxial Molecular Beam Radiofrequency Ring Electrode Ion Trap." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/242471.
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The dissertation focuses on the temperature dependent rate coefficient measurement of reactions in the interstellar medium using a coaxial molecular beam ring electrode ion trap apparatus. The first chapter introduces the previous studies of ion-molecule reactions in the ISM, the types of instruments mainly used in the reaction rate coefficient study, the former research on the ring electrode ion trap and the gas phase reaction mechanisms. Compare to other instruments, our molecular beam - ring electrode ion trap is extremely good at ion cooling and temperature control for both ions and neutral molecules. Chapter two describes each part of the instrument used in detail. Ions produced by electron impact in the ion source chamber, are mass filtered and then reach the ring electrode ion trap. In the trap, ions collide with molecules in the molecular beam where reaction takes place. When the reaction is done, all the ions remained in the trap (the reactant and product ions) come out and move to the detector. The molecular beam terminates at residual gas analyzer which is used for the number density calibration. The third chapter shows how the temperature of ions and molecules are controlled separately in order to find the reaction mechanism. Ions are cooled by the pulsed He buffer in the ring electrode trap and a chopped beam is used to make sure the ions are cooled to the desired low temperature when the reaction takes place. Chapters four to six describe the three reactions being studied using this instrument: N₂⁺ + H₂O charge transfer reaction, H₃O⁺ + C₂H₄ proton transfer reaction and H3O⁺ + (C₂H₂)₂/C₂H₂ dimer reaction. The temperature dependent rate coefficient data of these reactions are explained by the average dipole orientation theory, statistical theory and Colussi's acetylene dimer model, respectively. Two temperatures are defined and applied in the experimental rate coefficients analysis: ion-molecule center of mass collision temperature and the reaction statistical temperature which is based on the numbers of degrees of freedom of both reactants.
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Chang, Qiang. "Continuous-time random-walk simulation of surface kinetics." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1166592142.
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Ghesquière, Pierre. "Rôle des glaces interstellaires dans la complexité moléculaire de l’espace : modélisation par les méthodes de la chimie théorique." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS044/document.
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Les glaces du milieu interstellaire sont invoquées comme l'une des origines de la formation de molécules organiques complexes dans l'espace. En effet, elles constituent un support catalytique pour des réactions chimiques et pourraient ainsi expliquer la formation de molécules d'intérêt prébiotique. Toutefois, en raison de la faible température des milieux considérés, la vitesse de la réaction est contrainte par le déplacement des différentes réactifs l'un vers l'autre. L'objectif de cette thèse est donc de traiter la réactivité et la diffusion de molécules simples dans les glaces interstellaires. Je présente dans cette thèse les résultats de l'étude de la réaction entre le dioxyde de carbone et l'ammoniac dans les glaces interstellaires. Cette étude a été effectuée au Laboratoire Univers et Particules de Montpellier ; elle combine différentes méthodes de la chimie théorique et confronte les résultats avec ceux issus d'expériences que j'ai réalisées au Laboratoire de Physique des interactions Ioniques et Moléculaires de l'Université d'Aix-Marseille. Dans une première partie, des simulations de dynamique moléculaire classiques sont employées pour simuler un modèle de glace amorphe basse densité. Ce modèle est utilisé pour simuler la trajectoire de petites molécules (NH3, CO, CO2, H2CO) dans cette glace et en déduire des coefficients de diffusion à différentes températures. Ces résultats sont comparés à des résultats expérimentaux de diffusion du dioxyde de carbone ce qui valide la méthode théorique utilisée et permet de suggérer un mécanisme pour ce processus de diffusion. Dans une deuxième partie, la réaction entre le dioxyde de carbone et l'ammoniac est traitée dans le cadre de la théorie de la fonctionnelle densité par une approche « super-molécule ». Dans cette approche, le profil d'énergie et le mécanisme de la réaction dans des complexes moléculaires xNH3:CO2:yH2O sont étudiés. Deux produits de la réaction sont localisés : le carbamate d'ammonium et l'acide carbamique. La barrière d'énergie de la réaction obtenue est similaire à celle obtenue expérimentalement, et le carbamate d'ammonium est confirmé comme produit majoritaire de la réaction. Le profil d'énergie obtenu par cette approche « super-molécule » est ensuite étudié par dynamique moléculaire ab initio contrainte et le profil d'énergie libre est calculé par la méthode d'Intégration Thermodynamique. Cette approche confirme la forme générale du profil d'énergie et met en évidence un fort effet entropique du réseau d'eau. Je dresse finalement des conclusions sur les plans méthodologiques et astrochimiques permettant d'inscrire ma thèse dans des perspectives futures, notamment en incluant les barrières d'énergie de diffusion et de réaction, dans des modèles astrochimiques prenant en compte directement les réactions chimiques dans les glaces interstellairesIt is postulated nowadays that complex organic molecules in space form on the surface and in the volume of interstellar ices. These ices can catalyse chemical reactions what could explain the formation of prebiotic molecules. However, because of the low temperatures, the diffusion of the reactants one towards another is slow, limiting their reactivity. The objectif of this thesis is to treat the reactivity and the diffusion of simple molecules in interstellar ices. I present in this thesis the results of the study of the chemical reaction between carbon dioxide and ammonia in interstellar ices. This study was conducted in the Laboratoire Univers et Particules de Montpellier : it combines various theoretical chemistry methods and confront the results to experimental ones I participated in at the Laboratoire de Physique des Interactions Ioniques etMoléculaires of the Aix-Marseille university. In a first part, classical molecular dynamic simulations are used to simulate a low-density amorphous ice model and to calculate the diffusion coefficients at various temperatures of a series of small molecules (NH3, CO, CO2, H2CO). These results are compared to the experimental diffusion coeficients of the carbon dioxide validating the theoretical approach used and allowing to porpose a mechanism for the diffusion process. In a second part, the reaction between carbon dioxide and ammonia is studied in the frame of Density-Functional Theory using a « super-molecular » approach. In this approach, the reaction energy profile for the molecular complexes xNH3:CO2:yH2O, is studied. Two reaction products are localised : the ammonium carbamate and the carbamic acid. The reaction energy barrier obtained by these calculations is similar to the one obtained experimentally, and the ammonium carbamate is confirmed as the major reaction product. The obtained energy profile is therfore investigated by constrained ab initio molecular dynamics and the free energy profile is computed with the Thermodynamics Integration method. These calculations confirme the general form of the previous energy profile and enlight the strong entropic effect of the water network. Finally, conclusions are drawn, and perspectives on methodological as well as on astrochemical aspects, as the inclusion of the reaction and diffusion energy barriers I calculated in astrochemical models, are given
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Korsmeyer, Julie. "Anthracroronene in Astrophysical Water-Ice Analogs." Scholarship @ Claremont, 2019. https://scholarship.claremont.edu/scripps_theses/1413.
Full textAbstract:
Polycyclic aromatic hydrocarbons (PAHs) are the most abundant large organic molecules in space. They are thought to be the main contributor to the unidentified infrared (UIR) emission bands from the interstellar medium (ISM) for several reasons: UIR intensities correspond to carbon abundance, indicating the presence of a carbon-based molecule; UIRs are found in extremely harsh environments which means the source must be a stable molecule. The most important evidence is if the bands in mid-infrared (MIR) or 'fingerprint' region match those of PAHs. Through the infrared spectroscopy of matrix-isolated polycyclic aromatic hydrocarbons a compound's unique neutral and ionized vibrational modes can be identified. In this work, the PAH anthracoronene (AntCor, C36H18) is suspended in a matrix of water-ice, irradiated with ultraviolet (UV) light, and then analyzed using Fourier Transform Infrared (FTIR) spectroscopy. AntCor has not been studied in water ice before, and therefore the vibrational transition data collected (i.e. band positions and intensities) has been compared to coronene and anthracene, the parent molecules, and with theoretical predictions made using density functional theory. The data from this work will be incorporated into the NASA Ames PAH IR Database, where it will be applied to astronomical observations of the unidentified infrared emissions of the ISM, as well as observations of infrared absorption features in dense molecular clouds.
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Lin, Zhou. "Theoretical Studies on the Spectroscopy and Dynamics of Astrochemically Significant Species." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429633299.
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Fresneau, Aurélien. "Simulations expérimentales en laboratoire pour la préparation à l'analyse des données issues de missions spatiales, ainsi que pour l'étude de l'impact en exobiologie de l'évolution de la matière organique au sein d'environnements astrophysiques." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4760/document.
Full textAbstract:
Les grains de poussière se trouvant dans les nuages moléculaires denses jouent un grand rôle dans la formation de molécules organiques complexes. Ces grains sont recouverts d'un manteau glacé contenant des molécules primitives. Au cours de l'évolution des nuages moléculaires vers des systèmes planétaires, les grains sont soumis à des processus énergétiques transformant la matière organique présente dans les glaces. Les grains finissent par être intégrés dans les petits corps du système solaire tels que les comètes et les astéroïdes. Cette thèse cherche à simuler en laboratoire l'évolution chimique de ces glaces. Des analogues de ces glaces sont formés sur un substrat à basse température, et sont irradiés avec des photons UV et/ou réchauffés afin de simuler les processus astrophysiques. On forme ainsi un résidu organique que l'on caractérise grâce à la spectroscopie infrarouge à transformée de Fourier (IRTF) et la spectrométrie de masse à très haute résolution (VHRMS) par Orbitrap.Nous avons d'abord effectué des études mécanistiques centrées autour de la formation d'aminoalcools et d'hydroxynitriles lors du réchauffement de glaces contenant de l'acétaldéhyde (CH$_3$CHO) ou de l'acétone ((CH$_3$)$_2$CO) avec NH$_3$, HCN et H$_2$O. Nous avons ensuite étudié la composition globale de résidus issus de l'irradiation et du réchauffement de glaces contenant H$_2$O, CH$_3$OH, et NH$_3$. Nous présentons une nouvelle approche pour interpréter les données Orbitrap de ces résidus. Les similarités trouvées avec des analyses de matière organique météoritique issues de la littérature laissent à penser qu'une partie de son évolution pourrait être semblable à celle de nos résidusDust grains located in dense molecular clouds play a major role in the formation of complex organic molecules. These grains are covered by icy mantles containing primitive molecules. Dense molecular clouds can collapse and lead to the formation of planetary systems such as our own. During this evolution, the grains are exposed to energetic processes which transform the organic matter inside the ices. The grains are ultimately incorporated into small solar system bodies such as comets and asteroids, which can then contribute to the exogenous delivery of organic matter on Earth. In this context, this thesis focuses on simulating the chemical evolution of ices. To that end, ice analogues are formed by condensing a relevant gas mixture on a cold substrate. These interstellar ice analogues are irradiated with UV photons and/or heated in order to simulate astrophysical processes. An organic residue is formed which we characterized with Fourier transform infrared spectroscopy (FTIR) and very high resolution mass spectrometry (VHRMS) by Orbitrap.First, we performed mechanistic studies focused on the formation of aminoalcohols and hydroxynitriles from the warming of ices containing acetaldehyde (CH$_3$CHO) or acetone ((CH$_3$)$_2$CO) with NH$_3$, HCN and H$_2$O. Secondly, we studied the global composition of residues made from irradiation and warming of ices containing H$_2$O, CH$_3$OH, and NH$_3$. We present a new approach to interpret Orbitrap data of the residues. Similarities observed with meteoritic organic matter analyses found in the literature could mean that some of the evolution that led to meteoritic organic matter is shared with the evolution of our residues
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Lattelais, Marie. "Etudes théoriques à propos de l'origine exogène des molécules prébiotiques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00812072.
Full textAbstract:
La recherche de molécules prébiotiques dans le milieu interstellaire est importante pour comprendre le rôle potentiel de la chimie interstellaire dans la synthèse des molécules à l'origine de la vie. Aujourd'hui nous sommes confrontés à une apparente contradiction observationnelle : des acides aminés ont été identifiés dans les météorites mais aucun n'a été observé de façon certaine dans le milieu interstellaire. Dans un premier temps, nous utilisons les méthodes de calcul moléculaire DFT et ab-initio de la chimie quantique pour étudier la stabilité relative des isomères détectés dans le milieu interstellaire, ce qui nous conduit à établir un "Principe d'Energie Minimale" (PEM) stipulant que l'isomère le plus stable thermodynamiquement est le plus abondant. En s'appuyant sur ce principe, nous évaluons les possibilités de détection de nouvelles molécules prébiotiques dans le milieu interstellaire, en particulier les acides aminés. Puis, en suivant la même démarche, nous vérifions pour les météorites, que le lien entre abondance et ordre thermodynamique est respecté au niveau des acides aminés, ce qui nous permet de contraindre les conditions de formation dans les corps parents. Dans un second temps, nous utilisons les méthodes périodiques en ondes planes pour étudier les collages d'espèces moléculaires sur les grains carbonés et glacés interstellaires. Nous montrons l'existence d'une physisorption sélective pour certains types d'isomères. Elle entraînerait un biais observationnel sur les abondances relatives de ces isomères, ce qui nous donnerait une possibilité d'explication pour les quelques apparentes exceptions au PEM.
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Vinogradoff, Vassilissa. "Importance de la réactivité thermique au sein d'analogues de glaces interstellaires pour la formation de molécules complexes." Phd thesis, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00951946.
Full textAbstract:
Dans le milieu interstellaire (MIS) les grains de poussière jouent un rôle très important pour la chimie au sein des nuages moléculaires offrant une surface froide sur laquelle les atomes et molécules de la phase gazeuse vont s'accréter, formant un manteau de glace. Les nuages moléculaires sont caractérisés par des basses températures (10-50 K) et sont le lieu de formation des étoiles. Après effondrement gravitationnel du nuage suite à une trop forte densité en son sein, celui-ci devient le lieu de formation d'une nouvelle étoile. L'enveloppe autour de l'étoile évolue en disque dans lequel pourra se former des planètes, astéroïdes, comètes et autres objets d'un système planétaire. Durant cette formation stellaire, les glaces interstellaires (et les molécules qu'elles contiennent) sont alors soumises à plusieurs processus énergétiques (cycle de réchauffement, irradiations par des photons UV ou des particules chargées) qui vont affecter leurs compositions chimiques et finalement augmenter la complexité moléculaire avant leur incorporation dans les différentes objets du futur système planétaire. En laboratoire, afin de mieux comprendre l'évolution des molécules, composantes des glaces, nous avons développé une nouvelle approche qui consiste à réaliser des analogues "spécifiques" auxquels un seul processus énergétique à la fois est appliqué. Nous avons alors montré l'importance de l'effet thermique longtemps négligé pour la formation de molécules organiques complexes, montrant plusieurs implications astrophysiques et exobiologiques. Nos études permettent une meilleure compréhension des processus chimiques qui ont lieu dans la phase solide du MIS.
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Cazaux, Stéphanie Michelle. "Grain surface chemistry in astrophysical objects : from H₂ to complex molecules /." 2004. http://dissertations.ub.rug.nl/faculties/science/2004/s.m.cazaux/.
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Braakman, Rogier. "Gas-Phase Terahertz Spectroscopy and the Study of Complex Interstellar Chemistry." Thesis, 2010. https://thesis.library.caltech.edu/5284/1/thesis.pdf.
Full textAbstract:
Terahertz spectroscopy holds great promise in the advancement of the field of astrochemistry. The sensitive observation of interstellar THz radiation is expected to lower detection limits and allow the study of larger and more complex species than is currently possible at millimeter wavelengths, which will place further constraints on chemical models and permit a direct comparison to the organic compounds seen in carbonaceous chondrites. With the successful recent launch of the Herschel Space Telescope, which will give high-fidelity access to interstellar THz radiation for the first time, and the completion of the Atacama Large Millimeter Array (ALMA) by 2013, the THz astronomy era is upon us. Unfortunately, laboratory THz spectroscopy presents significant challenges and will be soon be lagging behind the newly available observational platforms. Technologies to extend the capabilities of high-resolution spectroscopic systems into the THz domain are actively being pursued on many fronts, but affordable systems that are broadly tunable, sensitive and achieve the necessary resolution are not yet available. The work in this thesis should therefore be seen as part of the effort in the transition from centimeter-/millimeter-wave to THz spectroscopy that is currently taking place in the astrochemistry community.
As part of this thesis, observational searches for the complex organics hydroxyacetone (CH₃COCH₂OH), 2-cyanoethanol (OHCH₂CH₂CN) and methoxyacetonitrile (CH₃OCH₂CN) were attempted at millimeter wavelengths. The unsuccessful nature of these searches highlight the current limits of studying interstellar chemistry using pure rotational spectroscopy. The characterization of the laboratory spectra of these molecules is nonetheless important as it will aid in the assignment and description of the rotational substructure and band shapes of their THz torsional spectra, features that may allow their interstellar detection; and this thesis presents methods by which such complex spectra may be rapidly and efficiently collected and fit using automated spectrometers and modern software tools.
The description of the spectrum of hydroxyacetone is furthermore of interest due to the presence of the very low barrier to internal rotation in this molecule. Many interstellar compounds, both known and potential future targets, have functional groups capable of internal rotation in their structure; and so the effort in understanding the complex effects of the low barrier rotor in this case will benefit the general effort to further understand internal rotation.
In searching for new interstellar molecules, both at millimeter wavelengths and at higher THz frequencies, characterization of the complete spectra of known interstellar molecules is of great importance to allow substraction of their contribution to observational spectra. In this thesis, the ground-state rotational spectrum of methanol, the most important "interstellar weed", is catalogued and described in detail through most of the THz region that will be accessible with Herschel and ALMA.
Lastly, as part of the effort to increase the sensitivity of THz spectrometers, the use of Fabry-Perot cavities at these frequencies is explored. Such resonant cavities hold the potential to significantly increase the possible path lengths in spectroscopic system and to allow novel and sensitive detection techniques. Optimal configurations and the limits on achievable path lengths and Q-factors of such cavities are discussed, as are the possible extensions of Fourier Transform MicroWave (FT-MW) techniques to THz frequencies.
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(8769668), Sean M. Fritz. "Applications of Multi-Resonance Broadband Rotational Spectroscopy to Interstellar and Combustion Chemistry." Thesis, 2020.
Find full textAbstract:
The chemical complexity of the interstellar medium and combustion environments pose a
challenge to the scientific community seeking to provide a molecular understanding of their
combustion. More refined spectroscopic tools and methodologies must be developed to selectively
detect and characterize the widening array of fuel and interstellar species. The direct relationship
between molecular structure and rotational frequencies makes rotational spectroscopy highly
structural specific; therefore, it offers a powerful means of characterizing polar molecules.
However, rotational spectra usually contain transitions from multiple components with multiple
conformations as well as other dynamical properties interleaved with one another, making the
assignment of the spectra very challenging. This thesis describes experimental work using
broadband microwave spectroscopy and vacuum ultraviolet time-of-flight mass spectrometry to
address a number of challenging problems in the spectroscopy of gas complex mixtures.In the first part of my work, we report details of the design and operation of a single apparatus
that combines Chirped-Pulse Fourier Transform Microwave spectroscopy (CP-FTMW) with VUV
photoionization Time-of-Flight Mass Spectrometry (VUV TOFMS). The supersonic expansion
used for cooling samples is interrogated first by passing through the region between two
microwave horns capable of broadband excitation and detection in the 2-18 GHz frequency region
of the microwave. After passing through this region, the expansion is skimmed to form a molecular
beam, before being probed with 118 nm (10.5 eV) single-photon VUV photoionization in a linear
time-of-flight mass spectrometer. The two detection schemes are powerfully complementary to
one another. CP-FTMW detects all components with significant permanent dipole moments.
Rotational transitions provide high-resolution structural data. VUV TOFMS provides a gentle and
general method for ionizing all components of a gas phase mixture with ionization thresholds
below 10.5 eV, providing their molecular formulae. The advantages, complementarity, and
limitations of the combined methods are illustrated through results on two gas-phase mixtures
made up of (i) three furanic compounds, two of which are structural isomers of one another, and
(ii) the effluent from a flash pyrolysis source with o-guaiacol as precursor.
The broadband spectrum of 3-phenylpropionitrile was recorded under jet-cooled
conditions over the 8-18 GHz region. A novel multi-resonance technique called strong field
coherence breaking (SFCB) was implemented to record conformer-specific microwave spectra. This technique involves sweeping the broadband chirp followed by selectively choosing a set of
single frequencies pulses to yield a set of rotational transitions that belong to a single entity in the
gas-phase mixture, aiding assignment greatly. Transitions belonging to anti and gauche
conformers were identified and assigned and accurate experimental rotational constants were
determined to provide insight on the molecular structure. Experimental rotational transitions
provided relative abundances in the supersonic expansion. A modified line picking scheme was
developed in the process to modulate more transitions and improve the overall efficiency of the
SFCB multiple selective excitation technique.
The rotational spectrum of 2-hexanone was recorded over the 8-18 GHz region using a CPFTMW spectrometer. SFCB was utilized to selectively modulate the intensities of rotational
transitions belonging to the two lowest energy conformers of 2-hexanone, aiding the assignment.
In addition, the SFCB method was applied for the first time to selectively identify rotational
transitions built off the two lowest energy hindered methyl rotor states of each conformer, 0a1 and
1e. Since these two states have rotational energy levels with different nuclear spin symmetries,
their intensities could be selectively modulated by the resonant monochromatic pulses used in the
SFCB method. The difference spectra, final fit and structural parameters are discussed for the three
assigned conformers of 2-hexanone.
Developing new experimental techniques that allow for species identification and
quantification in the high-temperature environment of reacting flows is a continuing challenge in
combustion research. Here, we combine broadband chirped-pulse microwave (rotational)
spectroscopy with an atmospheric-pressure jet-stirred reactor as a novel method to identify key
reactive intermediates in low-temperature and ozone-assisted oxidation processes. In these
experiments, the gas sample, after being withdrawn from reactive dimethyl ether/O2/Ar,
dimethoxy methane/O2/Ar, and ethylene/O2/O3/Ar mixtures, expands via a supersonic expansion
into the high vacuum of a microwave spectrometer, where the rotationally cold ensemble of polar
molecules is excited with short MW radiation frequency ramps (chirps). The response of the
molecular ensemble is detected in the time domain and after a Fourier transformation, the spectral
composition of the transient emission is obtained in the frequency domain. The observed rotational
frequencies are uniquely correlated to molecular structures and allow for an unambiguous
identification of the sampled species. Detection and identification of intermediates such as
formaldehyde, methyl formate, formic acid, formic acid anhydride, and the primary ethylene ozonide via literature-known rotational frequencies are evidence for the superb identification
capabilities of broadband chirped-pulse microwave spectroscopy. Strong-field coherence breaking
is employed to identify and assign transitions due to a specific component. The observation of van
der Waals complexes provides an opportunity to detect combustion intermediates and products
that are impossible to detect by rotational spectroscopy as isolated molecules.
Lastly, preliminary data on important combustion precursors is studied including pentanal,
trans-2-pentenal and o-,m- and p-vinylanisole. The rotational spectrum of these five molecules is
recorded from the 8-18 GHz region under jet-cooled conditions. For pentanal and trans-2-pentenal,
SFCB was utilized to dissect the broadband spectrum, identifying the four and two lowest energy
structures, respectively. The structural parameters and finals fits are provided.
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Beletsky, Yuri [Verfasser]. "Extragalactic molecular clouds and chemistry of diffuse interstellar clouds / vorgelegt von Yuri Beletsky." 2009. http://d-nb.info/997854502/34.
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McGuire, Brett Andrew. "Time-Domain TeraHertz Spectroscopy and Observational Probes of Prebiotic Interstellar Gas and Ice Chemistry." Thesis, 2015. https://thesis.library.caltech.edu/8598/1/mcguire_thesis_4.pdf.
Full textAbstract:
Understanding the origin of life on Earth has long fascinated the minds of the global community, and has been a driving factor in interdisciplinary research for centuries. Beyond the pioneering work of Darwin, perhaps the most widely known study in the last century is that of Miller and Urey, who examined the possibility of the formation of prebiotic chemical precursors on the primordial Earth [1]. More recent studies have shown that amino acids, the chemical building blocks of the biopolymers that comprise life as we know it on Earth, are present in meteoritic samples, and that the molecules extracted from the meteorites display isotopic signatures indicative of an extraterrestrial origin [2]. The most recent major discovery in this area has been the detection of glycine (NH2CH2COOH), the simplest amino acid, in pristine cometary samples returned by the NASA STARDUST mission [3]. Indeed, the open questions left by these discoveries, both in the public and scientific communities, hold such fascination that NASA has designated the understanding of our "Cosmic Origins" as a key mission priority.
Despite these exciting discoveries, our understanding of the chemical and physical pathways to the formation of prebiotic molecules is woefully incomplete. This is largely because we do not yet fully understand how the interplay between grain-surface and sub-surface ice reactions and the gas-phase affects astrophysical chemical evolution, and our knowledge of chemical inventories in these regions is incomplete. The research presented here aims to directly address both these issues, so that future work to understand the formation of prebiotic molecules has a solid foundation from which to work.
From an observational standpoint, a dedicated campaign to identify hydroxylamine (NH2OH), potentially a direct precursor to glycine, in the gas-phase was undertaken. No trace of NH2OH was found. These observations motivated a refinement of the chemical models of glycine formation, and have largely ruled out a gas-phase route to the synthesis of the simplest amino acid in the ISM. A molecular mystery in the case of the carrier of a series of transitions was resolved using observational data toward a large number of sources, confirming the identity of this important carbon-chemistry intermediate B11244 as l-C3H+ and identifying it in at least two new environments. Finally, the doubly-nitrogenated molecule carbodiimide HNCNH was identified in the ISM for the first time through maser emission features in the centimeter-wavelength regime.
In the laboratory, a TeraHertz Time-Domain Spectrometer was constructed to obtain the experimental spectra necessary to search for solid-phase species in the ISM in the THz region of the spectrum. These investigations have shown a striking dependence on large-scale, long-range (i.e. lattice) structure of the ices on the spectra they present in the THz. A database of molecular spectra has been started, and both the simplest and most abundant ice species, which have already been identified, as well as a number of more complex species, have been studied. The exquisite sensitivity of the THz spectra to both the structure and thermal history of these ices may lead to better probes of complex chemical and dynamical evolution in interstellar environments.
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Blanksby, Stephen J. (Stephen James). ""Gas phase synthesis of interstellar cumulenes : mass spectrometric and theoretical studies" / by Stephen J. Blanksby." 1999. http://hdl.handle.net/2440/19402.
Full textAbstract:
Copies of author's previously published articles inserted.Supplement entitled: Addressing referee concerns, stapled to back end paper (5 leaves).
Bibliography: leaves 199-212.
xii, 212 leaaves : ill. ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Presents methodologies for the synthesis of charged analogues of a number of molecular species residing in the large gas clouds which are present in regions of interstellar and circumstellar space. Quantum chemical calculations have been used to provide further insight into the structure and energetics of these molecules.
Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 1999
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Blanksby, Stephen J. (Stephen James). ""Gas phase synthesis of interstellar cumulenes : mass spectrometric and theoretical studies" / by Stephen J. Blanksby." Thesis, 1999. http://hdl.handle.net/2440/19402.
Full textAbstract:
Copies of author's previously published articles inserted.Supplement entitled: Addressing referee concerns, stapled to back end paper (5 leaves).
Bibliography: leaves 199-212.
xii, 212 leaaves : ill. ; 30 cm.
Presents methodologies for the synthesis of charged analogues of a number of molecular species residing in the large gas clouds which are present in regions of interstellar and circumstellar space. Quantum chemical calculations have been used to provide further insight into the structure and energetics of these molecules.
Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 1999
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Etim, Emmanuel Edet. "Computational Studies on Interstellar Molecular Species : From Formation to Detection." Thesis, 2016. http://etd.iisc.ac.in/handle/2005/3216.
Full textAbstract:
Initiated with the purpose of assigning the Fraunhofer lines in the solar spectrum to atomic transitions in the 18th century, the collaboration between spectroscopists and astrophysicists has remained fruitful, successful and ever fascinating. This collaboration has resulted in the unique detection of over 200 different molecular species in the interstellar medium (ISM). These interstellar molecular species play significant roles in diverse fields such as atmospheric chemistry, astrochemistry, prebiotic chemistry, astrophysics, astronomy, astrobiology, etc, and in our understanding of the solar system ''the world around us''. This Thesis work focuses on understanding of the different aspects of the chemistry of the various classes of these molecular species.
Chapter one starts with an historical perspective of what is now regarded as Molecular Astrophysics or Astrochemistry and discusses the interstellar medium and its properties; interstellar molecular species and their importance; molecular spectroscopy as an indispensible tool in interstellar chemistry and the different formation routes of these molecular species. It also discusses hydrogen bonding which is one of the most important of all the intermolecular interactions. The chapter ends by setting the stage for the present investigations.
The chapter two of the Thesis saddled with the task of describing the methodology employed in this Thesis begins by setting the stage on the importance of computational chemistry in interstellar chemistry. It discusses the Gaussian 09 suite of programs and the various theoretical methods used in all the quantum chemical calculations reported in this Thesis. The chapter ends with a brief summary on the homebuilt Pulsed Nozzle Fourier Transform Microwave (PN-FTMW) spectrometer used for the preliminary studies on Isoprene...Argon weakly bound complex reported in the appendix.
After the introductory chapters, chapter three begins with what is unarguably one of the most important classes of interstellar molecular species - 'interstellar isomers'. In this chapter, the Energy, Stability and Abundance (ESA) relationship existing among interstellar molecular species has been firmly established using accurate thermochemical parameters obtained with the composite models and reported observational data. From the relationship, “Interstellar abundances of related species are directly proportional to their stabilities in the absence of the effect of interstellar hydrogen bonding”. The immediate consequences of the relationship in addressing some of the questions in interstellar chemistry such as: Where are Cyclic Interstellar Molecules? What are the possible candidates for astronomical observation? Why are more Interstellar Cyanides than isocyanides? among others are briefly discussed. Following the ESA relationship, other studies addressing some of the whys and wherefores in interstellar chemistry are discussed in details. From ESA relationship, though there has not been any successful astronomical observation of any heterocycle, the ones so far searched remain the best candidates for astronomical observation in their respective isomeric groups. The observation of the first branched chain molecule in
ISM is in agreement with the ESA relationship and the C5H9N isomers have been shown to contain potential branched chain interstellar molecules. That molecules with the C-C-O backbone have less potential of formation in ISM as compared to their counterparts with the C-O-C backbone has been demonstrated not to be true following the ESA relationship. A detailed investigation on the relationship between molecular partition function and astronomical detection of isomeric species (or related molecules) shows that there is no direct correlation between the two rather there is a direct link between the thermodynamic stability of the isomeric species (or related molecules) and their interstellar abundances which influences the astronomical observation of some isomers at the expense of others.
Chapter four presents an interesting and a fascinating phenomenon among the interstellar molecular species as it discusses for the first time, the existence and effects of Interstellar Hydrogen Bonding. This interstellar hydrogen bonding is shown to be responsible for the deviations from thermodynamically controlled processes, delayed observation of the most stable isomers, unsuccessful observations of amino acids among other happenings in interstellar chemistry and related areas. On the prediction that ketenes are the right candidates for astronomical searches among their respective isomers, a ketenyl radical; HCCO has recently been detected in line with this prediction. The deviation from the rule that the ratio of an interstellar sulphur molecule to its oxygen analogue is close to the cosmic S/O ratio is well accounted for on the basis of hydrogen bonding on the surface of the dust grains. Detecting weakly bound complexes in ISM has not been a major interest in the field so far but the detectability of weakly bound complexes in ISM is very possible as discussed in this chapter. Following the conditions in which these complexes are observed in the terrestrial laboratory as compared to the ISM conditions; it suffices to say that weakly bound complexes are present and are detectable in ISM. They could even account for some of the 'U' lines.
Chapter five of the Thesis discusses the Linear Interstellar Carbon Chains which are the dominant theme in interstellar chemistry accounting for over 20% of all the known interstellar and circumstellar molecular species. Accurate spectroscopic parameters within experimental accuracy of few kHz which are the indispensable tools for the astronomical observation of these molecular species; are obtained for over 200 different species from the various chains using an inexpensive combined experimental and theoretical approach. With the availability of the spectroscopic parameters; thermodynamics is utilized in accounting for the known systems and in examining the right candidates for astronomical searches. These molecular species are shown to also obey the ESA relationship observed for the isomeric species discussed in chapter three of this work. The effect of kinetics on the formation processes of these molecular species is well controlled by thermodynamics as discussed in this chapter. Finally, the application of these studies in reducing the 'U' lines and probing new molecular species has been briefly summarized.
Chapter six discusses Interstellar Ions and Isotopologues which are two unique classes of interstellar molecular species. Different studies on interstellar ions and isotopologues are presented. From the studies on interstellar protonated species with over 100 molecular species; protonated species resulting from a high proton affinity prefers to remain protonated
rather than transferring a proton and returning to its neutral form as compared to its analogue that gives rise to a lower proton affinity from the same neutral species. The studies on detectable interstellar anions account for the known interstellar anions and predict members of the C2nO-, C2nS-, C2n-1Si-, HC2nN-, CnP-, and C2n chains as outstanding candidates for astronomical observation including the higher members of the C2nH- and C2n-1N- groups whose lower members have been observed. From high level ab initio quantum chemical calculations; ZPE and Boltzmann factor have been used to explain the observed deuterium enhancement and the possibility of detecting more deuterated species in ISM. Though all the heterocycles that have so far been searched for in ISM have been shown to be the right candidates for astronomical observation as discussed in the ESA relationship, they have also been shown to be strongly bonded to the surface of the interstellar dust grains thereby reducing their abundances, thus, contributing to their unsuccessful detection except for furan which is less affected by hydrogen bonding. The D-analogues of the heterocycles are shown from the computed Boltzmann factor to be formed under the dense molecular cloud conditions where major deuterium fractionation dominates implying very high D/H ratio above the cosmic D/H ratio which suggests the detectability of these deuterated species.
Chapter seven examines the isomerization of the most stable isomer (which is probably the most abundant) to the less stable isomer(s) as one of the plausible formation routes for interstellar molecular species. An extensive investigation on the isomerization enthalpies of 243 molecular species from 64 isomeric groups is reported. From the results, the high abundances of the most stable isomers coupled with the energy sources in interstellar medium drive the isomerization process even for relative enthalpy difference as high as 67.4 kcal/mol. Specifically, the cyanides and their corresponding isocyanides pairs appear to be effectively synthesized via this process. The following potential interstellar molecules; CNC, NCCP, c-C5H, methylene ketene, methyl Ketene, CH3SCH3, C5O, 1,1-ethanediol, propanoic acid, propan-2-ol and propanol are identified and discussed. In all the isomeric groups, isomerization appears to be an effective route for the formation of the less stable isomers (which are probably less abundant) from the most stable ones.
Chapter eight summarizes the conclusions drawn from the different studies presented in this Thesis and also highlights some of the future directions of these studies. The first appendix presents the preliminary study on Isoprene...Ar weakly bound complex while the second appendix contains a study on interstellar C3S describing the importance of accurate dipole moment in calculating interstellar abundances of molecular species and in astrophysical and astronomical models.
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Etim, Emmanuel Edet. "Computational Studies on Interstellar Molecular Species : From Formation to Detection." Thesis, 2016. http://hdl.handle.net/2005/3216.
Full textAbstract:
Initiated with the purpose of assigning the Fraunhofer lines in the solar spectrum to atomic transitions in the 18th century, the collaboration between spectroscopists and astrophysicists has remained fruitful, successful and ever fascinating. This collaboration has resulted in the unique detection of over 200 different molecular species in the interstellar medium (ISM). These interstellar molecular species play significant roles in diverse fields such as atmospheric chemistry, astrochemistry, prebiotic chemistry, astrophysics, astronomy, astrobiology, etc, and in our understanding of the solar system ''the world around us''. This Thesis work focuses on understanding of the different aspects of the chemistry of the various classes of these molecular species.
Chapter one starts with an historical perspective of what is now regarded as Molecular Astrophysics or Astrochemistry and discusses the interstellar medium and its properties; interstellar molecular species and their importance; molecular spectroscopy as an indispensible tool in interstellar chemistry and the different formation routes of these molecular species. It also discusses hydrogen bonding which is one of the most important of all the intermolecular interactions. The chapter ends by setting the stage for the present investigations.
The chapter two of the Thesis saddled with the task of describing the methodology employed in this Thesis begins by setting the stage on the importance of computational chemistry in interstellar chemistry. It discusses the Gaussian 09 suite of programs and the various theoretical methods used in all the quantum chemical calculations reported in this Thesis. The chapter ends with a brief summary on the homebuilt Pulsed Nozzle Fourier Transform Microwave (PN-FTMW) spectrometer used for the preliminary studies on Isoprene...Argon weakly bound complex reported in the appendix.
After the introductory chapters, chapter three begins with what is unarguably one of the most important classes of interstellar molecular species - 'interstellar isomers'. In this chapter, the Energy, Stability and Abundance (ESA) relationship existing among interstellar molecular species has been firmly established using accurate thermochemical parameters obtained with the composite models and reported observational data. From the relationship, “Interstellar abundances of related species are directly proportional to their stabilities in the absence of the effect of interstellar hydrogen bonding”. The immediate consequences of the relationship in addressing some of the questions in interstellar chemistry such as: Where are Cyclic Interstellar Molecules? What are the possible candidates for astronomical observation? Why are more Interstellar Cyanides than isocyanides? among others are briefly discussed. Following the ESA relationship, other studies addressing some of the whys and wherefores in interstellar chemistry are discussed in details. From ESA relationship, though there has not been any successful astronomical observation of any heterocycle, the ones so far searched remain the best candidates for astronomical observation in their respective isomeric groups. The observation of the first branched chain molecule in
ISM is in agreement with the ESA relationship and the C5H9N isomers have been shown to contain potential branched chain interstellar molecules. That molecules with the C-C-O backbone have less potential of formation in ISM as compared to their counterparts with the C-O-C backbone has been demonstrated not to be true following the ESA relationship. A detailed investigation on the relationship between molecular partition function and astronomical detection of isomeric species (or related molecules) shows that there is no direct correlation between the two rather there is a direct link between the thermodynamic stability of the isomeric species (or related molecules) and their interstellar abundances which influences the astronomical observation of some isomers at the expense of others.
Chapter four presents an interesting and a fascinating phenomenon among the interstellar molecular species as it discusses for the first time, the existence and effects of Interstellar Hydrogen Bonding. This interstellar hydrogen bonding is shown to be responsible for the deviations from thermodynamically controlled processes, delayed observation of the most stable isomers, unsuccessful observations of amino acids among other happenings in interstellar chemistry and related areas. On the prediction that ketenes are the right candidates for astronomical searches among their respective isomers, a ketenyl radical; HCCO has recently been detected in line with this prediction. The deviation from the rule that the ratio of an interstellar sulphur molecule to its oxygen analogue is close to the cosmic S/O ratio is well accounted for on the basis of hydrogen bonding on the surface of the dust grains. Detecting weakly bound complexes in ISM has not been a major interest in the field so far but the detectability of weakly bound complexes in ISM is very possible as discussed in this chapter. Following the conditions in which these complexes are observed in the terrestrial laboratory as compared to the ISM conditions; it suffices to say that weakly bound complexes are present and are detectable in ISM. They could even account for some of the 'U' lines.
Chapter five of the Thesis discusses the Linear Interstellar Carbon Chains which are the dominant theme in interstellar chemistry accounting for over 20% of all the known interstellar and circumstellar molecular species. Accurate spectroscopic parameters within experimental accuracy of few kHz which are the indispensable tools for the astronomical observation of these molecular species; are obtained for over 200 different species from the various chains using an inexpensive combined experimental and theoretical approach. With the availability of the spectroscopic parameters; thermodynamics is utilized in accounting for the known systems and in examining the right candidates for astronomical searches. These molecular species are shown to also obey the ESA relationship observed for the isomeric species discussed in chapter three of this work. The effect of kinetics on the formation processes of these molecular species is well controlled by thermodynamics as discussed in this chapter. Finally, the application of these studies in reducing the 'U' lines and probing new molecular species has been briefly summarized.
Chapter six discusses Interstellar Ions and Isotopologues which are two unique classes of interstellar molecular species. Different studies on interstellar ions and isotopologues are presented. From the studies on interstellar protonated species with over 100 molecular species; protonated species resulting from a high proton affinity prefers to remain protonated
rather than transferring a proton and returning to its neutral form as compared to its analogue that gives rise to a lower proton affinity from the same neutral species. The studies on detectable interstellar anions account for the known interstellar anions and predict members of the C2nO-, C2nS-, C2n-1Si-, HC2nN-, CnP-, and C2n chains as outstanding candidates for astronomical observation including the higher members of the C2nH- and C2n-1N- groups whose lower members have been observed. From high level ab initio quantum chemical calculations; ZPE and Boltzmann factor have been used to explain the observed deuterium enhancement and the possibility of detecting more deuterated species in ISM. Though all the heterocycles that have so far been searched for in ISM have been shown to be the right candidates for astronomical observation as discussed in the ESA relationship, they have also been shown to be strongly bonded to the surface of the interstellar dust grains thereby reducing their abundances, thus, contributing to their unsuccessful detection except for furan which is less affected by hydrogen bonding. The D-analogues of the heterocycles are shown from the computed Boltzmann factor to be formed under the dense molecular cloud conditions where major deuterium fractionation dominates implying very high D/H ratio above the cosmic D/H ratio which suggests the detectability of these deuterated species.
Chapter seven examines the isomerization of the most stable isomer (which is probably the most abundant) to the less stable isomer(s) as one of the plausible formation routes for interstellar molecular species. An extensive investigation on the isomerization enthalpies of 243 molecular species from 64 isomeric groups is reported. From the results, the high abundances of the most stable isomers coupled with the energy sources in interstellar medium drive the isomerization process even for relative enthalpy difference as high as 67.4 kcal/mol. Specifically, the cyanides and their corresponding isocyanides pairs appear to be effectively synthesized via this process. The following potential interstellar molecules; CNC, NCCP, c-C5H, methylene ketene, methyl Ketene, CH3SCH3, C5O, 1,1-ethanediol, propanoic acid, propan-2-ol and propanol are identified and discussed. In all the isomeric groups, isomerization appears to be an effective route for the formation of the less stable isomers (which are probably less abundant) from the most stable ones.
Chapter eight summarizes the conclusions drawn from the different studies presented in this Thesis and also highlights some of the future directions of these studies. The first appendix presents the preliminary study on Isoprene...Ar weakly bound complex while the second appendix contains a study on interstellar C3S describing the importance of accurate dipole moment in calculating interstellar abundances of molecular species and in astrophysical and astronomical models.
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Jackson, Douglas M. "Selected ion flow tube studies of interest to the chemistry of ion-molecule reactions in the interstellar medium." 2007. http://purl.galileo.usg.edu/uga%5Fetd/jackson%5Fdouglas%5Fm%5F200705%5Fms.
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