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Dissertations / Theses on the topic 'Atom molecule collision'

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Published: 4 June 2021

Last updated: 15 February 2022

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1

Beyene, Musie. "Magnetic field control of ultracold atom-molecule collision." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3196/.

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In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.

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2

Quichaud, Viviane. "Etude des processus elementaires : de synthese de la molecule no, en post-decharge en ecoulement, de collisions titane-gaz rares, titane-molecules, par perturbation laser resolue en temps." Paris 6, 1987. http://www.theses.fr/1987PA066135.

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I. Etude de la preparation des etats excites de no dans un dispositif de post-decharge en ecoulement a partir de n::(2) excite (prepare par transfert d'excitation a partir d'atomes ar metastables dans une decharge basse pression) et de o (obtenu par dissociation de o::(2) dans une decharge de he). Observation d'une emission intense des bandes gamma de no, qui implique un etat a courte duree de vie (b) de n::(2) et le premier etat metastable de o. Ii. Analyse des processus d'extinction et de transfert d'excitation a partir d'etats a courte duree de vie de ti (crees dans un dispositif a cathode creuse) lors de collisions avec des gaz rares (ar, ne, he) et des molecules (n::(2),h::(2)). Ces experiences permettent l'etude de cinetiques de reactions elementaires au sein d'un plasma basse pression ensemence de vapeurs metalliques, a l'aide du dispositif de post-decharge en ecoulement

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3

Gadea, Florent Xavier. "Theorie des hamiltoniens effectifs : applications aux problemes de diabatisation et de collision reactive." Toulouse 3, 1987. http://www.theses.fr/1987TOU30276.

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Etude approfondie sur la theorie des hamiltoniens effectifs et analyse de leurs applications aux methodes de diabatisation et au traitement des collisions reactives. Propositions pour le calcul des valeurs propres de l'hamiltonien par des methodes de perturbation ou iteratives, pour l'emploi d'hamiltoniens effectifs dans le calcul des surfaces quasi diabatiques et le traitement general des collisions reactives. Application a la reaction cs+h::(2) etudiee par les methodes ab initio pour la geometrie colineaire : surfaces de potentiel, sections efficaces et mecanismes predominants

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4

Girard, Bertrand. "Etude de la collision reactive ii + f -> if + i par fluorescence induite par laser." Paris 6, 1987. http://www.theses.fr/1987PA066398.

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Etude de cette collision par la methode des faisceaux croises et grace a la transition (b <- x) intense, dans le visible, apres analyse de la saturation du processus d'excitation laser de cette transition de if forme. Deduction des populations des differents niveaux rovibrationnels de l'etat x. Etablissement d'une cartographie detaillee de la distribution rotationnelle des niveaux vibrationnels v = 8 a 20 de l'etat x de if: aspect bimodal qui implique la coexistence de deux chemins reactionnels differents. Attribution a un artefact de l'important signal observe anterieurement pour v = 0. Mesures preliminaires de la section efficace differentielle par effet doppler

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5

Astruc, Jean-Pierre. "Transfert d'électron entre atomes excités et molécules dans une expérience en jets croisés avec fluorescence résolue dans le temps." Paris 13, 1987. http://www.theses.fr/1987PA132020.

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Etude experimentale avec résolution temporelle à l'échelle de la nanoseconde des valeurs absolues des séctions efficaces pour les transferts partiels d'énergie électronique entre Na(4d) et He, Ar, N(2), O(2), N(2)o et SF(6). Développement quantitatif de deux modèles à intermediaire ionique : réseau de multicroisement et diffusion résonnants atome excité-molecule. Emploi de l'approximation d'impact avec correction d'effet de coeur pour la transfert de moment orbital na(4d -> 4f)

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6

Rossi, François-Noël. "Etude théorique des collisions non réactives entre atomes alcalins et molécules d'hydrogène ou de deuterium : Calcul et analyse des surfaces de potentiel, application aux transitions de structure fine du rubidium." Paris 13, 1986. http://www.theses.fr/1986PA132015.

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Calcul des courbes de potentiel adiabatiques pour les géométries colinéaires et perpendiculaires, à l'aide d'un pseudopotentiel dépendant du moment orbital électronique et d'une approche à deux centres; bon accord avec les calculs ab initio existants. Examen des différentes symétries de ces systèmes dans le formalisme de la théorie des groupes, afin d'étudier les valeurs propres et facteurs propres de l'hamiltonien électronique. Calcul quantique des sections efficaces relatives des transitions de structure fine de Rb induites par collision avec H(2) ou D(2). En tenant compte des niveaux rotationnels moléculaires, obtention d'un très bon accord avec les résultats expérimentaux et interprétation de l'effet isotopique

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7

Lühr, Armin. "Collisions of low-energy antiprotons and protons with atoms and molecules." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16084.

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In dieser Arbeit wird eine, zeitabhängige, nicht störungstheoretische numerische Methode entwickelt, welche Ionisation und Anregung von Atomen oder Molekülen in Stößen mit entweder PB oder P beschreibt und auf der impact-parameter Methode basiert. Es wird eine spektrale close-coupling Methode verwendet, um die zeitabhängige Schrödinger-Gleichung zu lösen, in welcher die Wellenfunktion in (effektive) Ein- oder Zwei-Elektronen-Eigenzustände des Targets entwickelt wird. Dies beinhaltet auch eine erstmalige volle Zwei-Elektronen-Beschreibung von H2 in PB-Stößen. Rechnungen werden für PB-Stöße mit H, H2+ und H2 sowie He und den Alkaliatomen Li, Na, K und Rb durchgeführt. Daten für P-Stöße werden für H2 und die Alkaliatomen Li, Na und K erzielt. Die Methode wird durch einen detaillierten Vergleich der erhaltenen Ergebnisse für P-Stöße und für PB + He mit Literaturdaten verifiziert. Andererseits ergänzen die totalen und differentiellen Wirkungsquerschnitte für Ionisation und Anregung der Targets in PB-Stößen die spärliche Literatur. Sowohl die Resultate für verschiedene Targets als auch für PB- und P-Stöße werden miteinander verglichen. Ein Schwerpunkt dieser Arbeit liegt auf der Untersuchung von PB + H2, welche die Abhängigkeit der Wirkungsquerschnitte vom Kernabstand und von der relativen Ausrichtung der molekularen Achse beinhaltet. Weiterhin werden Ergebnisse mit Ein-Elektronen-Modellpotentialen erzielt und mit der vollen Zwei-Elektronen-Beschreibung von H2 verglichen. Außerdem werden Energieverluste in PB-Stößen bestimmt.
In this work a nonperturbative, time-dependent numerical approach is developed which describes ionization and excitation of atoms or molecules by either PB or P impact based on the impact-parameter method. A spectral close-coupling method is employed for solving the time-dependent Schrödinger equation in which the scattering wave function is expanded in (effective) one- or two-electron eigenstates of the target. This includes for the first time a full two-electron, two-center description of the H2 molecule in PB collisions. The radial part of the one-electron eigenstates is expanded in B splines while the two-electron basis is obtained with a configuration-interaction approach. Calculations are performed for PB collisions with H, H2+, and H2 as well as with He and alkali-metal atoms Li, Na, K, and Rb. Additionally, data are obtained for P collisions with H2, Li, Na, and K. The developed method is tested and validated by detailed comparison of the present findings for P impacts and for PB + He collisions with literature data. On the other hand, total and differential cross sections for ionization and excitation of the targets by PB impact complement the sparse literature data of this kind. Results gained from different targets as well as from PB and P impact are compared with each other and assessed. Furthermore, results obtained with one-electron model potentials are compared to the full two-electron description of H2. Finally, stopping powers for PB impacts are determined.

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8

Bull, James. "Application of Quantum Mechanics to Fundamental Interactions in Chemical Physics: Studies of Atom-Molecule and Ion-Molecule Interactions Under Single-Collision Conditions: Crossed Molecular Beams; Single-Crystal Mössbauer Spectroscopy: Microscopic Tensor Properties of ⁵⁷Fe Sites in Inorganic Ferrous High-Spin Compounds." Thesis, University of Canterbury. Department of Chemistry, 2010. http://hdl.handle.net/10092/4292.

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As part of this project and in preparation for future experimental studies of gas-phase ion-molecule reactions, extensive modification and characterization of the crossed molecular beam machine in the Department of Chemistry, University of Canterbury has been carried out. This instrument has been configured and some preliminary testing completed to enable the future study of gas-phase ion-molecule collisions of H⁺₃ and Y⁻ (Y = F, Cl, Br) with dipole-oriented CZ₃X (Z = H, F and X = F, Cl, Br). Theoretical calculations (ab initio and density functional theory) are reported on previously experimentally characterized Na + CH₃NO₂, Na + CH₃NC, and K + CH₃NC systems, and several other systems of relevance. All gas-phase experimental and theoretical studies have the common theme of studying collision orientation dependence of reaction under singlecollision conditions. Experimental measurements, theoretical simulations and calculations are also reported on some selected ferrous (Fe²⁺) high-spin (S=2) crystals, in an attempt to resolve microscopic contributions of two fundamental macroscopic tensor properties: the electric-field gradient (efg); and the mean square displacement (msd) in the case when more than one symmetry related site of low local point-group symmetry contributes to the same quadrupole doublet. These determinations have been made using the nuclear spectroscopic technique of Mössbauer spectroscopy, and complemented with X-ray crystallographic measurements.

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9

BERGNES, BRASEY CHANTAL. "Etude des processus directs elastique et inelastiques se produisant lors de la collision entre un ion d'helium et une cible d'hydrogene, pour une energie variant de 1,5 a 30 kev." Toulouse 3, 1988. http://www.theses.fr/1988TOU30204.

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Etude des sections efficaces doublement differentielles des processus elastiques et inelastiques au cours de la collision d'un faisceau d'ions de he avec h ou h::(2), entre 1,5 et 30 kev, pour des angles de diffusion compris entre 5' et 30**(o), par spectrometrie de perte d'energie du projectile. Comparaison des resultats a des valeurs calculees et mesurees anterieurement a d'autres auteurs. Proposition d'un modele permettant d'interpreter les resultats pour la cible h

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10

Horton, Timothy Scott. "COLLISIONAL AND RADIATIVE RELAXATION IN SODIUM DIMER AND ARGON ATOM COLLISIONS." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1480693544113525.

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11

Radouani, Abdelhak. "Réaction des atomes métastables de gaz rares (Ar*(3p2,0), Kr*(3p2) et Xe*(3p2)) avec le silane." Grenoble 1, 1986. http://www.theses.fr/1986GRE10143.

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Etude des produits de reactions par spectrometrie d'emission et de si a l'etat fondamental pas spectrometrie d'absorption. Absence d'emission dans le cas de xe et observation de la formation de si dans differents etats electroniques excites et de sih dans son 1er etat electronique excite, pour lesquels on determine les coefficients de chimiluminescence. Avantages de la technique de post-decharge en ecoulement. Emploi d'un modele statistique pour interpreter l'evolution des populations des niveaux rotationnels de sih**(*) par collision avec ar

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12

Boutalib, Abderrahim. "Etude théorique de la surface de potentiel du système HO::(2) + H. : Influence de la corrélation électronique." Pau, 1986. http://www.theses.fr/1986PAUU3009.

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Calcul des géométries du points de sille et des barrières d'activation pour les réactions d'abstraction (HO::(2) + H->H::(2) + O::(2)) et d'approche concertée (HO::(2) + H->H::(2)O + O) pour la méthode SDCI à l'ordre d'une base DZ dans la région de valence, augmentée par des orbitales de polarisation de type D sur chaque atome O. Evaluation des paramètres cinétiques dans le cadre de la théorie de l'état de transition : énergies d'activation et constantes de vitesse. Faible probabilité du mécanisme de réaction concertée

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13

Hérault, Joël. "Etude experimentale du ralentissement d'ions lourds de 20 a 100 mev par nucleon dans la matiere." Toulouse 3, 1988. http://www.theses.fr/1988TOU30075.

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Etude experimentale a l'aide d'ions lourds de l'accelerateur ganil sur le spectrometre lise (analyse en energie et en angle) pour determiner le pouvoir d'arret de 11 cibles gazeuses avec une incertitude de plus ou moins 3%. Mise en evidence d'une disparition de la difference entre pouvoirs d'arret des materiaux solides et gazeux lorsque la charge de l'ion tend vers son numero atomique. Analyse des distributions en energies pour de nombreux ions (de l'oxygene au molybdene) et analyse de la distribution angulaire dans des cibles solides et gazeuses. Comparaison des donnees experimentales aux calculs quantiques et classiques

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14

Glass, John T. "Relativistic ion-atom collision processes." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282153.

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15

Nagy, O. Z. I. "Analysis of electron-atom and electron-molecule collisions." Thesis, University of Stirling, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370537.

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16

Campbell, Eleanor Elizabeth Bryce. "Electronic and vibrational excitation in atom/molecule collisions." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/13295.

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17

O'Rouke, Sheelagh Francesca Camille. "Theory of ion-atom collisions." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334486.

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18

Suraud, Marie-Gabrielle. "Etude par spectrométrie X (10 [angström] [inférieur ou égal à] [lamda] [inférieur ou égal à] 100 [angström]) de l'échange de charge lors de collision à basse énergie, entre un ion multichargé et une cible neutre." Grenoble 1, 1988. http://www.theses.fr/1988GRE10038.

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Mesures des valeurs absolues des sections efficaces d'emission de rayons x, dont on deduit les valeurs absolues des sections efficaces de capture, pour les systemes c**(6+)-he,h::(2), n**(7+)-he,h::(2), o**(8+)-he,h::(c). Pour les projectiles a 2 electrons dans l'etat metastable 1s2s **(3)s, l'echange de charge peut s'accompagner de l'excitation de l'electron "2s" de l'ion incident vers des etats 1s2pnl **(3)p avec une probabilite variant suivant le systeme de collision, l'echange de charge simple restant preponderant dans tous les cas

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19

Osborne, Mark Allen. "Rotational transfer in diatomic and polyatomic molecules." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239696.

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20

Abbas, Isam Ahmed. "Studies of the dynamics of ion molecule collisions using cross beam technique." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/10787.

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21

McCartney, Mark. "Ionization processes in multielectron ion-atom collisions." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359106.

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22

Mowrey, Richard Carlton. "Theoretical studies of inelastic molecule-surface and resonant electron-atom and electron-molecule scattering /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu148725958026243.

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23

Hami, Mohamed. "Spectroscopie du mélange helium-xénon : rôle du monoxyde de carbone : analyse cinétique dans l'ultra-violet lointain." Toulouse 3, 1988. http://www.theses.fr/1988TOU30169.

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Etude spectroscopique des gaz purs et des melanges he-xe, excites par des particules alpha , entre 110 et 600 nm. Dans he observations de transitions moleculaires a 164 et 365 nm, et, en presence de co, du 1er systeme negatif (absence de v'=2). Dans xe, observation de deux continuums en uv proche et lointain et de la 2eme raie de resonance. Dans les melanges he-xe, observation en plus de la 1ere raie de resonance de xe avec renforcement des emissions de he par xe. Dans les melanges ne-co, emission du 1er systeme negatif et du 4eme systeme positif de l'ion et de la molecule; renforcement des emissions par addition de xe. Etude cinetique du 2nd continuum de xe dans les melanges he-xe a 173 nm (importance des processus heteronucleaires pour l'emission de l'excimere de xe) et du 4eme systeme positif dans les melanges ne-co (processus reactionnels a deux corps)

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24

Forster, Christine. "Aspects of charge exchange in ion-atom collisions." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6189/.

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The straight line semi-classical Impact Parameter method has been modified for use with classical trajectories. Ion-atom collisions have been modelled using wavefunctions expanded in terms of atomic basis states which were centred on either the target or projectile ions. Total and differential charge exchange cross-sections are presented for (^4)He(^++) and (^4)He(^+) collisions within the centre of mass energy range 0.21 kev < E(_em) < 2.5 keV. Results using curved and straight line paths are compared with data from other authors. Significant trajectory effects were found at the lower energies in the range. The curved trajectory results were lower than those from the straight line model and also lower than previous calculations carried out. At higher energies in the range there was good agreement between straight line and curved trajectory models and previous work. Differential cross-sections were found to be sensitive to the trajectories employed, and comparisons have been made with previous work. Total, state specific and differential cross- sections for charge exchange are presented for Be(^++) and H collisions using a five state basis, within the centre of mass energy range 0.111 keV < E(_em) < 0.4444 keV. There was reasonable agreement between the straight line results and previous work. There were significant trajectory effects for all the final charge transfer states. Results are presented for low-energy collisions between positively charged muons and atomic hydrogen. An eight state basis has been used. Direct excitation cross sections for n = 2 atomic states and charge transfer cross sections to Is and n = 2 have been calculated. The effect on the cross sections of using different internuclear potentials has been examined. Trajectory effects were small for charge transfer to Is but were more pronounced in the direct excitation and charge exchange cross- sections to n = 2. These results have been compared to those obtained for curved trajectory H(^+) and H collisions at the same relative velocity, to assess the validity of velocity scaling. It was found that velocity scaling was reliable for charge transfer to Is and for total electron capture cross-sections. However, it was progressively inaccurate for direct excitation and for electron capture into excited states for µ(^+) impact energies of less than 300 eV. These results are discussed and suggestions for further work are made.

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25

Brawley, S. J. "Collisions of positronium with atoms and molecules." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/18988/.

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Positronium, Ps, is the atom-like bound state of an electron and its antimatter counterpart, the positron. This work encompasses the experimental techniques required to produce a collimated beam of Ps atoms and recent investigations of Ps collisions on a variety of atomic and molecular targets to determine Ps total and fragmentation cross-sections. For the former experiment, the present work is compared to theory - for which there is now very good agreement for low energy Ps–He collisions - and to other projectiles where the present data shows that total cross-sections for equivelocity Ps and electrons are nearly identical for a wide range of targets and velocities. The Ps fragmentation measurements proceed via the detection of ejected electrons or positrons for Ps collisions on Xe at 18 and 30 eV. Detection of ejected positrons is a unique signature of Ps fragmentation and the recent integrated measurements for this process agree well with theory, as do the shapes of the differential cross-sections with respect to the longitudinal energy of the ejected positrons. Concerning these, the energy dependence of the positron distributions appear similar for the present measurements on Xe and those previously measured for a He target. When detecting ejected electrons, the experiment is sensitive to reactions in which the projectile and/or target are ionised, and the integrated cross-sections indicate that target-ionisation is significant at only ∼3 eV above threshold in Xe.

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26

Hughes, Timothy John. "Luminescent collisions of energetic manganese atoms." Thesis, Northumbria University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262819.

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27

Støchkel, Kristian. "Electron-transfer processes in fast ion-atom collisions." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-732.

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28

McLaughlin, Thomas Kevin. "Excited state formation in slow multiply-charged ion-atom collisions." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317515.

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29

Blackwood, Jennifer Elizabeth. "Positronium scattering by the noble gases." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343099.

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30

McGrath, C. "Fundamental collisions of hydrogen ions with atoms and molecules." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395440.

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31

Hodgkinson, Jacqueline. "Study of slow multiply charged ion-atom collisions using translational energy spectroscopy." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318774.

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32

Colla, Massimiliano. "Experiments with a metastable helium atomic trap /." View thesis entry in Australian Digital Theses Program, 2006. http://thesis.anu.edu.au/public/adt-ANU20060828.104229/index.html.

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33

Elliott, David Samuel. "Collisions of ions and electrons with simple atoms." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317114.

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34

Eyles, Chris J. "An experimental and theoretical study of the dynamics of atom-molecule scattering." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d887db09-915e-4b3b-80e0-e9f1684518db.

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In this thesis, a joint experimental and theoretical study of the dynamics of atom- molecule collisions will be presented. The focus of this study will be conducted towards the precise, quantitative theoretical description of the collision dynamics in terms of the vectors k, k', j, and j' (the incoming and outgoing relative momenta associated with the collision, and the initial and final rotational angular momentum of the target diatom respectively) that define the collision, and on the experimental measurement of these vector correlations. Chapter 1 is introductory, providing an overview of the field of reaction dynamics, and the experimental and theoretical methods that exist to treat the collisions of atoms and molecules. This work focusses on the collisions of the spherically symmetric rare gas atoms Ar and He with the open-shell heteronuclear diatomic radicals NO and OH. In particular, the fully quantum state-to-state resolved differential cross-sections for the collisions of NO(X) with Ar (reflecting the k - k' vector correlation), and the collisional cross-sections for the depolarisation of the rotational angular momenta of the NO(A) and OH(A) radicals (reflecting the j - j' vector correlation) have been determined experimentally and theoretically, and the results have been discussed and interpreted in terms of the mechanistic aspects of the collision dynamics, and the features of the potential energy surface that give rise to these. In Chapter 2, the atom-molecule systems that constitute the subject of this work will be introduced in detail. The close-coupled quantum mechanical and quasi-classical trajectory scattering calculations performed as part of this work will be discussed in greater detail, providing a greater insight into molecular scattering theory. The explicit calculation of the quantities of interest (most significantly the differential cross-section, and the tensor/depolarisation cross-sections) will be presented for the quasi-classical and quantum cases, offering the most transparent definitions of these quantities. Finally the mathematical description of the spatial probability distribution of a single vector, a pair of correlated vectors, and three correlated vectors is described in detail, including a discussion of the quantum mechanical nature of the vectors in question. Chapter 3 describes the experimental measurement of the differential cross-sections for the collisions of NO(X) with Ar. A hexapole was used to select uniquely those NO molecules in the |Ω = 0.5; j = 0.5, f> quantum state, allowing full experimental quantum state-to-state selection for the first time. A crossed molecular beam apparatus with (1+1') resonantly enhanced multi-photon ionisation detection coupled with velocity mapped ion- imaging was employed to measure the differential cross-section, and the details of the experimental set-up are provided. The accurate extraction of the true, centre of mass frame differential cross-section from the laboratory frame information yielded by the experiment is something of an involved process, and much of this Chapter will be concerned with the development of a Monte Carlo method to achieve this end. In Chapter 4, the experimental and theoretical fully quantum state-to-state resolved differential cross-sections for the collisions of NO(X) with Ar are presented, having been measured for the first time. Full resolution of the initial parity of the rotational wave- function of the NO molecule has enabled the observation of parity dependent structures within the differential cross-section, and the origin of these structures has been investi- gated, employing quasi-classical, quantum mechanical and semi-classical methods in order to elucidate the mechanism by which they arise. Chapter 5 introduces the measurement of the collisional depolarisation of the rotational angular momentum of the diatom. Rate constants for the collisional depolarisation of j were measured by monitoring the time dependence of the amplitude of Zeeman and hyperfine quantum beats in the (1+1) laser induced fluorescence decays of an ensemble of NO(A) or OH(A) radicals in the presence of a series of background pressures of a collision partner. The creation and subsequent evolution of the polarisation of j induced by the absorption of polarised laser light is described, and the magnitude of this polarisation is linked to the amplitude of the quantum beat in the laser induced fluorescence decay. The extraction of the depolarisation cross-sections from the raw experimental data is discussed, and a Monte Carlo simulation of the experiment is described to account for any additional unwanted experimental factors that may contribute to the loss of polarisation of j. A formalism is also introduced that makes use of the tensor opacities to recover spin- rotation conserving and spin-rotation changing open-shell rotational energy transfer and depolarisation cross-sections from the intrinsically closed shell quasi-classical trajectory scattering calculations. In Chapter 6, the experimentally determined collisional depolarisation cross-sections for the collisions of NO(A) with He/Ar, and of OH(A) with Ar at collision energies of 39 meV/757meV are presented along with their theoretical counterparts. The relative magnitudes of the cross-sections are rationalised in terms of the potential energy surface over which the collision takes place, and the importance of spin-rotation conserving and spin-rotation changing transitions in the depolarisation process is assessed. A detailed study of the ensemble of quasi-classical trajectories is performed to determine the character of the various atom-molecule collisions, and to identify which conditions lead to the most efficient depolarisation of j. The relative importance of the potential energy surface and the collision kinematics is also assessed at this point. The results presented in this thesis thus investigate two complementary expressions of the collision dynamics, the k - k' and j - j' vector correlations, and encompass a variety of collision partners exhibiting vastly differing collision characteristics. As such, this work serves as an illustrative overview of atom-molecule scattering dynamics, containing both experimental and theoretical reflections of the collision dynamics, and relating this information back to the fundamentals of scattering theory.

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Antunes, Rodrigo Augusto Ferreira. "The role of halouracils in radiotherapy studied by electron transfer in atom-molecule collisions experiments." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/6653.

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Dissertação para obtenção do Grau de Doutor em Engenharia Física
The role of ionising radiation as a source of damage to living tissues and cells has been recognized as a key issue regarding cellular DNA integrity and, ultimately, mutagenesis. The lethal effect of radiation, despite being most of the time undesired, can sometimes be useful, as is the case of radiation therapy. However, still the major concern in medicine is that only the cancerous cell material should be destroyed, keeping as much as possible healthy tissue unaffected. One way to control this damage seems to be the application of radiosensitizers that are incorporated into cancer cells. The cancer tissue doped with these radiation sensitizing molecules may be destroyed preferentially under radiation exposure, in very well defined places and even with radiation doses which may be low enough to prevent healthy cell material to be affected in the surrounding medium. This leads to nanodosimetry and so the sorts of interactions have now to be described at the molecular level. Upon irradiation, the most abundant secondary species produced along the radiation track are low energy electrons and so the study of electron induced damage to biological relevant molecules seems indubitably relevant. The research described in this thesis covers for the first time the study of electron transfer on two halouracils (5-chlorouracil and 5-fluorouracil) and isolated DNA/RNA basis (thymine and uracil)by atom-molecule collisions. In order to investigate such molecules, a crossed beam experiment, comprising a neutral potassium beam and a biolomecular effusive beam, was improved and a time-offlight mass spectrometer implemented allowing for the detection of negative ion formation following electron transfer processes in atom-molecule collisions. In these experiments the anionic fragmentation patterns and formation yields were obtained. These results are shown to be significantly different from the dissociative electron attachment (free electrons) results, unveiling that the damaging potential of secondary electrons to biomolecules can be somewhat underestimated. In addition, the halouracils sensibility to electron induced damage appears to be enhanced with respect to thymine and uracil, which may be extremely relevant as it reinforces their effectiveness as radiosensitizer molecules.
Portuguese Foundation for Science and Technology - SFRH/BD/32271/2006

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36

Roberts, Gareth. "Collisional processes of laser-excited alkaline earth atoms." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.346405.

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37

Smith, Andrew Michael. "Theoretical studies of long-range collisions between laser cooled atoms." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315816.

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38

Luxford, Thomas Frederick Murray. "The stereodynamics of the inelastic collisions of NO(A2Σ+) with atoms and molecules." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3318.

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Please note that the equations are not displaying correctly below. Please see the full text instead. A newly constructed crossed molecular beam velocity map imaging experiment is used to study vector correlations for the rotationally inelastic collisions of NO(A2Σ+) with a range of atoms and diatomic molecules. Measurements are made of the differential cross section (DCS), and the { }2 +qA (θ) moments. Where possible, the experimental vector correlations are compared to the results of quantum scattering (QS) calculations performed on literature ab initio potential energy surfaces (PESs). Collisions of NO(A) with Ar and Ne lead to distinct features in the DCS, with a sharp, forward-scattered peak caused by scattering through the attractive region of the PES, and broader, higher-angle rotational rainbow peaks caused by scattering through the repulsive region of the PES. Sharp, angle-dependent fluctuations are observed in the { } 2 + qA (θ) moments. While there is generally good agreement between the experimental and QS results, deviations in the QS DCS highlight inaccuracies in the literature PESs. Collisions of NO(A) with He are controlled entirely through interactions on the repulsive region of the PES. Excellent agreement between experiment and QS calculations was found for both the DCS and {2} q+ A (θ) moments, showing that the literature PES is accurate. Collisions of NO(A) with D2 produced results similar to He, showing that the uncalculated NO(A)-D2 PES is similar to the NO(A)-He PES. Differences in the experimental results for the two systems were used to provide details on the differences between the two PESs. DCSs and {2} q+ A moments are successfully recorded for the collisions of NO(A) with N2, O2 and CO as a function of rotational excitation of the unobserved partner. Trends in the DCSs for different degrees of rotational energy transfer to the unobserved collision partner are found to be consistent with collisions with the repulsive region of the PES leading to quenching collisions, rather than rotational energy transfer.

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39

Pradhan, Atul D. (Atul Deep). "Photodissociation of molecular ions and low-energy collisions of atoms and ions." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/17317.

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40

Seach, K. J. A. "A study of non-adiabatic processes in ion-atom and ion-molecule collisions by beam techniques in the 100eV energy range." Thesis, University of Edinburgh, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.661713.

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The characterisation and commissioning of a new molecular beam apparatus is described. This equipment was designed to have the capability of observing coincidence signals between photon emission detection and scattered particle detection resulting from ion-molecular and ion- atom collisions. Early experiments involving the observation of photon emission, which resulted from non adiabatic charge exchange processes in He⁺/Ar collisions, are detailed, A mechanism is proposed for the excitation of the ²p ^o and ²D ^o states of Ar⁺. in those collisions. Excitation resulting from charge exchange processes in the He⁺/HC1 collision system are also described. In particular a strong non Franck-Condon effect is observed in the excitation of the HC1⁺ A ^2Σ+ state. The unexpectedvibrational population of the HC1⁺ A ^2Σ+ state is examinedunder a variety of conditions and is contrasted to the vibrational distribution of that state resulting from collisions between Ar⁺ and HC1. A mechanism is proposed which accounts for these findings. Finally the principles and execution of the first coincidence experiment are described. This experiment involved the observation of emission from the N₂C^3πustate, excited in collision with He⁺, and recording the time differential between the detection of those photons and the detection of the associated scattered ions. The results of this experiment are detailed and suggestions made as to the reasons for our failure to observe a clear result.

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41

McCaig, Clive. "Low-energy ion-atom collisions : 1) travelling molecular orbitals and vibrational translations factors and 2) autoionisation to two interacting continua." Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268177.

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42

Ben, bouchrit Ridha. "Etude théorique des collisions moléculaires réactives de type atome + molécule polyatomique." Thesis, Besançon, 2015. http://www.theses.fr/2015BESA2037/document.

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Nous avons étudié les collisions réactives O(1D) + CH4 et O(1D) + H2O d’intérêt atmosphérique et astrophysique à l’aide de méthodes de chimie quantique et de dynamique réactionnelle. Pour la première réaction, des calculs de dynamique quantique à l’aide d’une méthode indépendante du temps ont été entrepris sur une surface d’énergie potentielle existante en considérant CH3 comme un pseudo-atome. Cette approche à dimensionnalité réduite, qualifiée ici de modèle pseudo-triatomique, a permis d’obtenir les probabilités de réaction à un moment angulaire total nul (J=0), puis de calculer les sections efficaces et les taux de réaction par une méthode approchée de type J-shifting. Nos résultats quantiques ont été comparés aux résultats obtenus par une méthode quasi-classique de trajectoires et aux prédictions expérimentales. Ces comparaisons ont, entre autre, validé le fait que la voie de sortie OH + CH3 était la voie principale pour cette réaction. La seconde réaction O(1D) + H2O a été abordée d’un point de vue structure électronique. Nous avons caractérisé les grandes lignes de la surface d’énergie potentielle de H2O2 en tenant compte de tous les degrés de liberté avec une méthode de calcul de haut niveau (MRCI : Multi Reference Configuration Interaction). Ainsi, nous avons pu déterminer avec une grande précision les géométries, les fréquences et les énergies des isomères du système H2O2 ainsi que son diagramme énergétique. A l’avenir, il faudra construire une surface d’énergie potentielle qui sera utilisée pour décrire la dynamique de cette réaction
We have studied the reactive collisions, O (1D) + CH4 and O (1D) + H2O, of atmospheric and astrophysical interest, using different quantum chemistry methods and reaction dynamics approaches. For the first reaction, quantum dynamical calculations using a time-independent method were carried out on an existing potential energy surface by considering CH3 as a pseudo-atom. This reduced dimensionality approach, i.e. a pseudo triatomic model, yielded the calculation of the reaction probabilities at zero total angular momentum (J = 0). The cross sections and reaction rates have been computed by the approximate J-shifting method. Our quantum results were compared with results obtained by a quasi-classical trajectory method and experimental predictions. These comparisons, among others, have enabled the fact that the channel CH3 + OH was the main exit channel for this reaction. The second reaction O(1D) + H2O has been studied at the level of electronic structure. We have characterized the outline of the potential energy surface of H2O2 , taking into account all the degrees of freedom at a high level calculation (MRCI: Multi Reference Configuration Interaction). Thus, we were able to determine with great accuracy the geometries, frequencies and energies of isomers of the H2O2 system and its energy diagram. In the future, a potential energy surface has to be built to be used in the dynamical calculations for this reaction

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43

Agueny, Hicham. "Etude théorique des processus électroniques ayant lieu au cours de collisions atomiques et moléculaires : approches non perturbatives." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-01021304.

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Deux domaines différents de la physique des collisions ont fait l'objet de mes travaux de thèse réalisés dans le cadre d'une cotutelle entre l'Université Moulay Ismail, Meknes-Maroc et l'Université Pierre et Marie Curie, Paris-France: le premier concerne les collisions ion-atome/molécule dans le régime des énergies intermédiaires (keV), alors que le second vise le domaine des collisions électron-atome assistées par un champ laser intense. Bien que distincts, les deux thèmes sont interconnectés puisqu'il s'agit principalement d'étudier, dans des approches non-perturbatives, les phénomènes de diffusion et la dynamique électronique des collisions de cibles atomiques et moléculaires soumis à de fortes et très courtes perturbations. La première partie porte spécifiquement sur la modélisation des processus de transfert électronique et d'ionisation induits lors de collisions d'ions et de cibles atomiques et moléculaires. L'étude porte particulièrement sur les phénomènes d'interférences de type Young, de multi-diffusion et de diffraction Fraunhofer observés au cours de ces processus. La deuxième partie de thèse repose sur une étude des processus de diffusion élastiques et inélastiques induits lors de collisions assistées par un champ laser intense. L'étude s'appuie sur l'analyse spécifique des transitions "libre-libre" au cours lesquelles la cible reste dans son état fondamental après la collision, et des phénomènes de résonance dans le processus d'excitation simultanée électron-photon de la cible.

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44

Grishkevich, Sergey. "Ultracold collisions in traps." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16098.

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Die ultrakalte Atom- und Molekülephysik, zu welcher man zum Beispiel bei der Bose-Einstein-Kondensation von verdünnten Gasen Zugang hat, wurde untersucht. In solchen Systemen dominieren Zwei-Körper-Stöße und ihre detaillierte Untersuchung ist eines der zentralen Themen dieser Arbeit. Diese wurden durchgeführt unter Berücksichtigung von elementaren chemischen Reaktionen, Photoassoziation und magnetischen Feshbach-Resonanzen. Weiterhin wurden Untersuchungen von Atomen in optischen Gittern durchgeführt. Die Viel-Teilchen-Systeme wurden nicht nur mit dem üblichen mean-field Ansatz behandelt, sondern auch darüber hinausgehend, um die voll korrelierte Bewegung zu simulieren.
The ultracold atomic and molecular physics as it is accessible, e.g., in Bose-Einstein condensates of dilute gases was investigated. In such systems two-body collisions are dominant and their detailed study is one of the central topics of this work. They were done considering elementary chemical reactions as photoassociation, and magnetic Feshbach resonances. Additionally, studies of atoms in optical lattice sites were carried out. The many-body systems were not only considered within the usually adopted mean-field approach but also beyond that in order to simulate the fully correlated motion.

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45

Marbach, Johannes [Verfasser]. "Quantum-Kinetic Modeling of Electron Release in Low-Energy Surface Collisions of Atoms and Molecules / Johannes Marbach." Greifswald : Universitätsbibliothek Greifswald, 2013. http://d-nb.info/1029509840/34.

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46

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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47

Sheach, Keith. "A study of non-adiabatic processes in ion/atom and ion/molecule collisions by beam techniques in the 100eV to 1000eV energy region." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/14400.

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The characterisation and commissioning of a new molecular beam apparatus is described. This equipment was designed to have the capability of observing coincidence signals between photon emission detection and scattered particle detection resulting from ion-molecular and ion- atom collisions. Early experiments involving the observation of photon emission, which resulted from non adiabatic charge exchange processes in He⁺/Ar collisions, are detailed, A mechanism is proposed for the excitation of the ²p ^o and ²D ^o states of Ar⁺. in those collisions. Excitation resulting from charge exchange processes in the He⁺/HC1 collision system are also described. In particular a strong non Franck-Condon effect is observed in the excitation of the HC1⁺ A ^2Σ+ state. The unexpectedvibrational population of the HC1⁺ A ^2Σ+ state is examinedunder a variety of conditions and is contrasted to the vibrational distribution of that state resulting from collisions between Ar⁺ and HC1. A mechanism is proposed which accounts for these findings. Finally the principles and execution of the first coincidence experiment are described. This experiment involved the observation of emission from the N₂C^3πustate, excited in collision with He⁺, and recording the time differential between the detection of those photons and the detection of the associated scattered ions. The results of this experiment are detailed and suggestions made as to the reasons for our failure to observe a clear result.

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48

Sherstov, Ivan V. "Matter wave interferences of potassium molecules and the influence of collisions with potassium atoms in the ground state." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981904947.

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49

Almeida, Diogo Alexandre Fialho de. "The role of electron transfer in DNA building blocks: evaluation of strand breaks and their implications." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/10875.

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Dissertação para obtenção do Grau de Doutor em Engenharia Física
Radiation-induced damage to biological systems, both direct and indirect processes, has increasingly come under scrutiny by the international scientific community due to recent findings that electrons are a very effective agent in damaging DNA/RNA. Indeed, much remains to be discovered regarding the exact physico-chemical processes that occur in the nascent stages of DNA/RNA damage by incident radiation. However, it is also known that electrons do not exist freely in the physiological medium, but rather solvated and/or pre-solvated states. This leads to the need for new techniques that can better explore the damaging role of “bound” electrons to DNA/RNA. The work presented in this thesis consists on the study of electron transfer in collisions of atomic species with molecules of biological relevance. In order to study these processes, two experimental setups were used. One setup consists of a crossed beam experiment where a neutral potassium beam is created and made to collide with an effusive molecular target beam. The anionic products that stem from electron transfer in potassium atom to the molecular target collisions are then extracted and time-of-flight (TOF) mass analysed. In the second setup a beam of anionic species is formed and made to collide with a molecular target. Collisions with three different anionic beams were performed (H-, O- and OH-), as well as with different simple organic molecules, by measuring the positive and negative ion fragmentation patterns with a quadrupole mass spectrometer (QMS). A comparison between these two collisional systems can greatly help to understand the underlying mechanisms of the electron transfer processes. Finally, studies of potassium collisions with sugar surrogates D-Ribose and THF were performed. These studies show very different fragmentation patterns from DEA, although in the case of THF, it is suggested that the initially accessed states are the same as in DEA. With these studies was also possible to show for the first time collision induced site and bond selectivity breaking, where the electron is transferred into a given state of the acceptor molecule and the resulting fragmentation pathways are exclusive to the initial anionic state. Furthermore, the role of the potassium cation post collisionwas explored and indeed its presence is suggested to induce at least partial suppression of auto-detachment. The implications that ensue from this degradation are analysed in the light of the obtained fragmentation patterns.

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50

Allen, John. "Theoretical atomic collision studies : electron transfer to doubly charged carbon ions and the exitation of the lithium atoms by slow hydrogen impact." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386730.

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