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1
Williams, Christopher F. "Wavepacket calculations on the reaction NOâ‚‚ + OH." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437004.
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Sharp, J. R. "Reactive scattering calculations in hyperspherical coordinates." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234214.
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Beyer, Adrian Nikolas. "On-the-fly instanton calculations of reaction rates." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708459.
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Frost, R. J. "Combining transition state theory with quasiclassical trajectory calculations." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233984.
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A new method of using quasiclassical trajectories to study the dynamics of elementary reactions is described. Trajectories are initiated in the phase space of a suitably chosen transition state and run forwards and backwards in time from the same starting point to simulate a complete collision. Calculations on a wide range of collinear A+BC reactions involving vibrationally excited reagents reveal that the optimum choice of transition state is a periodic orbiting dividing surface (pods) for which the action over one cycle of the pods is (v+0.5)h The method is extended to three dimensional reactions using the adiabatic periodic reduction scheme to find pods on fixed angle potential surfaces. The complete transition state is defined by joining these pods together. Methods for pseudorandomly sampling the transition state are described and the combined transition state theory-quasiclassical trajectory (TST-QCT) method is applied to the H+H2(v), N+N2(v) and F+H2(v = O) reactions at constant temperature. The TST-QCT method produces relative quantities directly, absolute values are readily obtained using transition state theory. The results of the new method are compared with conventional quasiclassical trajectory studies in the literature. Agreement is very good and the combined method brings about a very great saving in computer time by eliminating trajectories which fail to reach the strong interaction zone as well as revealing the extent of vibrational adiabaticity between reagents and the transition state. Finally, a modification to the TST-QCT method to allow the simulation of fixed collision energy reactions is described and tested on the F+H2 reaction.
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Kazemi, Masoud. "Calculations of Reaction Mechanisms and Entropic Effects in Enzyme Catalysis." Doctoral thesis, Uppsala universitet, Beräkningsbiologi och bioinformatik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316497.
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Ground state destabilization is a hypothesis to explain enzyme catalysis. The most popular interpretation of it is the entropic effect, which states that enzymes accelerate biochemical reactions by bringing the reactants to a favorable position and orientation and the entropy cost of this is compensated by enthalpy of binding. Once the enzyme-substrate complex is formed, the reaction could proceed with negligible entropy cost. Deamination of cytidine catalyzed by E.coli cytidine deaminase appears to agree with this hypothesis. In this reaction, the chemical transformation occurs with a negligible entropy cost and the initial binding occurs with a large entropy penalty that is comparable to the entropic cost of the uncatalyzed reaction. Our calculations revealed that this reaction occurs with different mechanisms in the cytidine deaminase and water. The uncatalyzed reaction involves a concerted mechanism and the entropy cost of this reaction appears to be dominated by the reacting fragments and first solvation shell. The catalyzed reaction occurs via a stepwise mechanism in which a hydroxide ion acts as the nucleophile. In the active site, the entropy cost of hydroxide ion formation is eliminated due to pre-organization of the active site. Hence, the entropic effect in this reaction is due to a pre-organized active site rather than ground state destabilization. In the second part of this thesis, we investigated peptide bond formation and peptidyl-tRNA hydrolysis at the peptidyl transferase center of the ribosome. Peptidyl-tRNA hydrolysis occurs by nucleophilic attack of a water molecule on the ester carbon of peptidyl-tRNA. Our calculations showed that this reaction proceeds via a base catalyzed mechanism where the A76 O2’ is the general base and activates the nucleophilic water. Peptide bond formation occurs by nucleophilic attack of the α-amino group of aminoacyl-tRNA on the ester carbon of peptidyl-tRNA. For this reaction we investigated two mechanisms: i) the previously proposed proton shuttle mechanism which involves a zwitterionic tetrahedral intermediate, and ii) a general base mechanism that proceeds via a negatively charged tetrahedral intermediate. Although both mechanisms resulted in reasonable activation energies, only the proton shuttle mechanism found to be consistent with the pH dependence of peptide bond formation.
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XUE, YUAN. "Quantum Mechanical Calculations on Ring-opening Reactions of Hexachlorophosphazenes." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627595429444473.
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Zhang, Jinmei. "Accurate Calculations of Molecular Properties with Explicitly Correlated Methods." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/50144.
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Conventional correlation methods suffer from the slow convergence of electron correlation energies with respect to the size of orbital expansions. This problem is due to the fact that orbital products alone cannot describe the behavior of the exact wave function at short inter-electronic distances. Explicitly correlated methods overcome this basis set problem by including the inter-electronic distances (rij) explicitly in wave function expansions. Here, the origin of the basis set problem of conventional wave function methods is reviewed, and a short history of explicitly correlated methods is presented. The F12 methods are the focus herein, as they are the most practical explicitly correlated methods to date. Moreover, some of the key developments in modern F12 technology, which have significantly improved the efficiency and accuracy of these methods, are also reviewed.
In this work, the extension of the perturbative coupled-cluster F12 method, CCSD(T)F12, developed in our group for the treatment of high-spin open-shell molecules (J. Zhang and E. F. Valeev, J. Chem. Theory Comput., 2012, 8, 3175.), is also documented. Its performance is assessed for accurate prediction of chemical reactivity. The reference data include reaction barrier heights, electronic reaction energies, atomization energies, and enthalpies of formation from the following sources: (1) the DBH24/08 database of 22 reaction barriers (Truhlar et al., J. Chem. Theory Comput., 2007, 3, 569.), (2) the HJO12 set of isogyric reaction energies (Helgaker et al., Modern Electronic Structure Theory, Wiley, Chichester, first ed., 2000.), and (3) the HEAT set of atomization energies and heats of formation (Stanton et al., J. Chem. Phys., 2004, 121, 11599.). Two types of analyses were performed, which target the two distinct uses of explicitly correlated CCSD(T) models: as a replacement for the basis-set-extrapolated CCSD(T) in highly accurate composite methods like HEAT and as a distinct model chemistry for standalone applications. Hence, (1) the basis set error of each component of the CCSD(T)F12 contribution to the chemical energy difference in question and (2) the total error of the CCSD(T)F12 model chemistry relative to the benchmark values are analyzed in detail. Two basis set families were utilized in the calculations: the standard aug-cc-p(C)VXZ (X = D, T, Q) basis sets for the conventional correlation methods and the cc-p(C)VXZ-F12 (X = D, T, Q) basis sets of Peterson and co-workers that are specifically designed for explicitly correlated methods. The conclusion is that the performance of the two families for CCSD correlation contributions (which are the only components affected by the explicitly correlated terms in our formulation) are nearly identical with triple- and quadruple-ζ quality basis sets, with some differences at the double-ζ level. Chemical accuracy (~4.18 kJ/mol) for reaction barrier heights, electronic reaction energies, atomization energies, and enthalpies of formation is attained, on average, with the aug-cc-pVDZ, aug-cc-pVTZ, cc- pCVTZ-F12/aug-cc-pCVTZ, and cc-pCVDZ-F12 basis sets, respectively, at the CCSD(T)F12 level of theory. The corresponding mean unsigned errors are 1.72 kJ/ mol, 1.5 kJ/mol, ~ 2 kJ/mol, and 2.17 kJ/mol, and the corresponding maximum unsigned errors are 4.44 kJ/mol, 3.6 kJ/mol, ~ 5 kJ/mol, and 5.75 kJ/mol.
In addition to accurate energy calculations, our studies were extended to the computation of molecular properties with the MP2-F12 method, and its performance was assessed for prediction of the electric dipole and quadrupole moments of the BH, CO, H2O, and HF molecules (J. Zhang and E. F. Valeev, in preparation for submission). First, various MP2- F12 contributions to the electric dipole and quadrupole moments were analyzed. It was found that the unrelaxed one-electron density contribution is much larger than the orbital response contribution in the CABS singles correction, while both contributions are important in the MP2 correlation contribution. In contrast, the majority of the F12 correction originates from orbital response effects. In the calculations, the two basis set families, the aug-cc-pVXZ (X = D, T, Q) and cc-pVXZ-F12 (X = D, T, Q) basis sets, were also employed. The two basis set series show noticeably different performances at the double-ζ level, though the difference is smaller at triple- and quadruple-ζ levels. In general, the F12 calculations with the aug-cc- pVXZ series give better results than those with the cc-pVXZ-F12 family. In addition, the contribution of the coupling from the MP2 and F12 corrections was investigated. Although the computational cost of the F12 calculations can be significantly reduced by neglecting the coupling terms, this does increase the errors in most cases. With the MP2-F12C/aug-cc-pVDZ calculations, dipole moments close to the basis set limits can be obtained; the errors are around 0.001 a.u. For quadrupole moments, the MP2-F12C/aug-cc-pVTZ calculations can accurately approximate the MP2 basis set limits (within 0.001 a.u.).Ph. D.
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Hlophe, Linda D. "Separable Representation of Nucleon-Nucleus Optical Potentials as Input to (d,p) Reaction Calculations." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1467319283.
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Huarte, Larrañaga Fermín. "Some insights on theoretical reaction dynamics: Use of absorbing potentials and exact three-dimensional calculations." Doctoral thesis, Universitat de Barcelona, 1999. http://hdl.handle.net/10803/2767.
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En la tesis doctoral se detallan los trabajos realizados en el marco del estudio de la dinámica de reacciones químicas elementales. La tesis está estructurada de modo que primero se muestran los resultados obtenidos para las reaccionesMg+FH, MgF+H y B+OH, BO+H mediante el método mecano-cuántico aproximado R-IOSA. En ambos casos son importantes los efectos de naturaleza mecano-cuántica en la reactividad. A continuación, se presentan varios trabajos realizados para incorporar potenciales absorbentes a las técnicas propagativas empleadas para resolver la dinámica de reacción.
Además de los detalles más técnicos que implican dicha implementación, en la tesis se indican diferentes pruebas acerca de la estabilidad y fiabilidad de dicha metodología. También se muestran resultados y prestaciones del método para varias reacciones (Mg+FH, Li+FH, H+F2,Cl+HCl y Ne+H2+).
Finalmente, se incluyen una serie de trabajos realizados en el contexto de un estudio mecano-cuántico exacto de la reacción Ne+H2+ NeH++H. Este estudio es por si solo destacable debido a la dificultad que entraña la resolución exacta de las ecuaciones de la dinámica de reacción. Los resultados obtenidos manifiestan una remarcable dependencia de fenómenos de naturaleza cuántica, en concreto de resonancias causadas por complejos metaestables formados durante la colisión.
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Aumond, João Paulo. "A model for the calculations of solvent effects on reaction rates for process design purposes." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85280.
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Grosman, Sergey. "Adaptivity in anisotropic finite element calculations." Doctoral thesis, Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600815.
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When the finite element method is used to solve boundary value problems, the
corresponding finite element mesh is appropriate if it is reflects the behavior of the true solution. A posteriori error estimators are suited to construct adequate meshes. They are useful to measure the quality of an approximate solution and to design adaptive solution algorithms. Singularly perturbed problems yield in general solutions with anisotropic features, e.g. strong boundary or interior layers. For such problems it is useful to use anisotropic meshes in order to reach maximal order of convergence. Moreover, the quality of the numerical solution rests on the robustness of the a posteriori error estimation with respect to both the anisotropy of the mesh and the perturbation parameters.
There exist different possibilities to measure the a posteriori error in the energy norm for the singularly perturbed reaction-diffusion equation. One of them is the equilibrated residual method which is known to be robust as long as one solves auxiliary local Neumann problems exactly on each element. We provide a basis for an approximate solution of the aforementioned auxiliary problem and show that this approximation does not affect the quality of the error estimation.
Another approach that we develope for the a posteriori error estimation is the hierarchical error estimator. The robustness proof for this estimator involves some stages including the strengthened Cauchy-Schwarz inequality and the error reduction property for the chosen space enrichment.
In the rest of the work we deal with adaptive algorithms. We provide an overview of the existing methods for the isotropic meshes and then generalize the ideas for the anisotropic case. For the resulting algorithm the error reduction estimates are proven for the Poisson equation and for the singularly perturbed reaction-difussion equation. The convergence for the Poisson equation is also shown.
Numerical experiments for the equilibrated residual method, for the hierarchical
error estimator and for the adaptive algorithm confirm the theory. The adaptive
algorithm shows its potential by creating the anisotropic mesh for the problem
with the boundary layer starting with a very coarse isotropic mesh.
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Yamamoto, Takeshi. "Theoretical study on the mode-specific unimolecular dissociation reaction HFCO→HF+CO by quantum dynamics calculations." 京都大学 (Kyoto University), 2000. http://hdl.handle.net/2433/181139.
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Calvo, Sergio Rafael. "Reactivity and stability of platinum and platinum alloy catalysts toward the oxygen reduction reaction." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2457.
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Peck, Jamie. "A combined approach of electronic structure calculations and spectroscopy for elucidating reaction mechanisms in organic and bioinorganic systems." Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/42360/.
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This thesis describes the use of density functional theory (DFT) to assist the interpretation of advanced spectroscopic techniques such as stopped flow Fourier transform infrared spectroscopy (FTIR), muon spin resonance (�SR), and nuclear inelastic scattering (NIS). These complementary techniques are used to investigate the structure and mechanism of a variety of important chemical systems, some of which are relevant to biological energy transduction and energy harvesting. The mechanisms by which [FeFe] and [NiFe] hydrogenase enzymes catalyse the reversible reduction of protons to dihydrogen are of intrinsic interest in the context of a developing hydrogen technology for energy transduction. Gas phase DFT calculations are used to simulate and assign structure to experimental solution phase FTIR spectra for a family of [FeFe]-hydrogenase model complexes. Further, the Mulliken charge distribution across the Fe centres are compared for di�erent dithiolate bridge groups and PMe3 ligand positions. In the pursuit of understanding the protonation mechanism of [FeFe]-hydrogenases, transition state theory is used and the energetics of reaction pathways leading to terminal and bridging hydrides calculated and compared. NIS demonstrates great potential for characterising the [FeFe]-hydrogenase mimics. In order to further develop and validate the technique, a combination of NIS, DFT calculations, FTIR and Raman spectroscopies are applied to a small Fe(III) model system in order to provide complete a characterisation of the low frequency metal
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Brinne, Roos Johanna. "Reaction dynamics on highly excited states." Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-27122.
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In this thesis I have performed theoretical studies on the reaction dynamics in few-atom molecules. In particular, I have looked at reaction processes in which highly excited resonant states are involved. When highly excited states are formed, the dynamics becomes complicated and approximations normally used in chemical reaction studies are no longer applicable.To calculate the potential energy curve for some of these states as a function of internuclear distance, a combination of structure calculations and scattering calculations have to be performed, and the reaction dynamics on the potentials has been studied using both time-independent and time-dependent methods.The processes that have been studied and which are discussed in this thesis are ion-pair formation in electron recombination with H3+, dissociative recombination and ion-pair formation of HF+, mutual neutralization in H++F- collisions and dissociative recombination of BeH+. Isotope effects in these reactions have also been investigated. Our calculated cross sections are compared with experimentally measured cross sections for these reactions.
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Guerra, André. "Modeling Mild Thermal Cracking of Heavy Crude Oil and Bitumen with VLE Calculations." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38003.
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The current shortage of crude oil from conventional sources has increased interest in developing unconventional resources such as oil sands. Heavy crudes and bitumen are found in Northern Alberta and their exploration, processing, and transport to market pose challenges in the use of these resources. Part of the solution to these challenges involves the reactive thermal processing of heavy crudes and bitumen. This thesis focused on mild thermal cracking reactions, and two studies regarding these reactions were presented.
The first was an experimental study performed in a pilot-scale semi-batch reactor. The three crude oils were heated to 350, 400, 425, and 450°C at 1240 kPa. A five-lump reaction model combined with a process simulator with VLE calculations was fitted with the experimental data obtained. The goodness of fit between the model predicted values and experimental values for the Hardisty (MBL), Albian Heavy Synthetic (AHS), and Christina Lake Dilute Bitumen (CDB) were determined to be 0.99, 0.99, and 0.98, respectively. Moreover, 80, 85, and 89% of the optimized model’s predicted values had less than 10% error for MBL, AHS, and CDB, respectively.
The second study described the implementation of a mild thermal cracking reaction model to the development of a train car fire-model for the assessment of safety aspects in the design of train cars used to transport crude oil. Case studies were conducted using the UniSim® depressuring utility and a previously developed mild thermal cracking reaction model to demonstrate the effect of compositional change. Three crude oils with varying properties and representative of the types of crudes transported by rail in Canada were used here: MBL, AHS, and CDB. The case studies conducted showed the performance of a train car fire-model to be dependent on the crude oil characteristics: up to -57% and -99% difference in model predicted variables for AHS and CDB, respectively, when compared to MBL. Furthermore, the model’s performance was also shown to be affected by the compositional change of a given crude oil due to mild thermal cracking reactions: up to 42% difference in model predicted variables when compared to the base case.
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Uzun, Alper. "Quantum Chemical Simulation Of No Reduction By Ammonia (scr Reaction) On V2o5 Catalyst Surface." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1090430/index.pdf.
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The reaction mechanism for the Selective Catalytic Reduction (SCR) of NO
by NH3 on V2O5 surface was simulated by means of density functional theory
(DFT) calculations performed at B3LYP/6-31G** level.
As the initiation reaction, ammonia activation on V2O5 was investigated.
Coordinate driving calculations showed that ammonia is adsorbed on Brønsted acidic V-OH site as NH4 + species by a nonactivated process with a relative energy of -23.6kcal/mol. Vibration frequencies were calculated as 1421, 1650, 2857 and 2900cm-1 for the optimized geometry, in agreement with the experimental literature. Transition state with a relative energy of -17.1kcal/mol was also obtained. At the end of the Lewis acidic ammonia interaction calculations, it was observed that ammonia is hardly adsorbed on the surface. Therefore, it is concluded that the SCR reaction is initiated more favorably by the Brø
nsted acidic ammonia adsorption. As the second step of the SCR reaction, NO interaction with the preadsorbed NH4 + species was investigated. Accordingly, NO interaction results in the formation of gas phase NH2NO molecule with a relative energy difference of 6.4kcal/mol. For the rest of the reaction sequence, gas phase decomposition of NH2NO was considered. Firstly, one of the hydrogen atoms of NH2NO migrates to oxygen. It then isomerizes in the second step. After that, the reaction proceeds with the isomerization of the other hydrogen. Finally, a second hydrogen atom migration to the oxygen leads to the formation of N2 and H2O. Total relative energy for this reaction series was obtained as -60.12kcal/mol, in agreement with the literature.
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Kadi, Malin. "Ultrafast Photo-induced Reaction Dynamics of Small Molecules." Doctoral thesis, Uppsala University, Department of Physical Chemistry, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3597.
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The main focus of this thesis is the investigation of the dissociation dynamics of aryl halides using femtosecond pump-probe spectroscopy. In the monohalogenated aryl halides, iodo-, bromo- and chlorobenzene, the rate of dissociation following excitation at 266 nm in the gas phase increased with increasing mass of the halogen atom. This process was assigned to predissociation of the initially excited singlet (π, π*) state via a repulsive triplet (n, σ*) state due to spin-orbit interaction. In addition to the predissociative mechanism, a direct dissociation channel was observed in iodobenzene. The rate of the predissociation in bromobenzene was found to be faster in the condensed phase than in the gas phase, which can be explained by solvent-induced symmetry perturbations. Ab initio calculations of the potential energy surfaces of the ground state and several low lying excited states in bromobenzene have been performed in order to verify the suggested mechanism. Substituting one of the hydrogen atoms in bromobenzene affected the predissociation rate significantly. In o-, m- and p-dibromobenzene the predissociation rate increased with decreasing distance between the bromine atoms in accordance with an increased spin-orbit interaction introduced by the bromine substituent. The fastest predissociation rate was observed in 1,3,5-tribromobenzene. With chlorine and fluorine substitution, inductive and conjugative effects were found to be of importance. In the o- and m-isomers of the dihalogenated aryl halides, an additional faster dissociation channel was observed. Guided by ab initio calculations of the potential energy surfaces in the dibromobenzene isomers, we ascribed the fast dissociation pathway to predissociation of an initially excited triplet state. Upon methyl group substitution in bromobenzene, the decreased lifetime of the initially excited state was attributed to an incresaed density of coupled states.
Another system which has been studied in the condensed phase is diiodomethane. Using Car-Parrinello molecular dynamics simulations we observed a prompt dissociation and subsequent recombination to the isomer, iso-diiodomethane, in acetonitrile solution.
Vibrational wavepacket dynamics in the C (1Σ+) state of NaK were studied using a direct ionization probing scheme. A simple analytical expression for the pump-probe signal was developed in order to see what factors that govern direct ionization of the vibrational wavepacket. Our experimental data was consistent with a photoionization transition dipole moment that varies with internuclear distance.
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Pinelo, Laura F. "An Investigation of the Thermal and Photochemical Reaction Mechanisms of Cycloalkenes and Ferrocenes with Ozone by Matrix Isolation Spectroscopic Analysis and Theoretical Calculations." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427981459.
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Rogge, Torben. "Experimental and Computational Studies on Ruthenium- and Manganese-Catalyzed C-H and C-C Activation." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/21.11130/00-1735-0000-0005-1298-B.
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Karpov, Yevhen. "Solution Processable Conducting Films based on Doped Polymers:." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-230794.
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Hoops, Michael Dean. "Matrix Isolation Studies of Photochemical and Thermal Reactions of Cyclic Organic Substrates with Chromyl Chloride and Ozone/O Atoms." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1211558149.
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Soyer, Sezen. "Quantum Chemical Simulation Of Nitric Oxide Reduction By Ammonia (scr Reaction) On V2o5 / Tio2 Catalyst Surface." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606632/index.pdf.
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The reaction mechanism for the selective catalytic reduction (SCR) of nitric oxide by ammonia on (010) V2O5 surface represented by a V2O9H8 cluster was simulated by density functional theory (DFT) calculations. The computations
indicated that SCR reaction consisted of three main parts. In the first part ammonia activation on Brønsted acidic V-OH site as NH4+ species by a nonactivated process takes place. The second part includes the interaction of NO with pre-adsorbed NH4 + species to eventually form nitrosamide (NH2NO). The rate limiting step for this part as well as for the total SCR reaction is identified as NH3NHO formation reaction. The last part consists of the decomposition of NH2NO on the cluster which takes advantage of a hydrogen transfer mechanism between the active V=O and V-OH groups. Water and ammonia adsorption and dissociation are investigated on (101) and (001) anatase surfaces both represented by totally fixed and partially relaxed Ti2O9H10 clusters. Adsorption of H2O and NH3 by H-bonding on previously H2O and NH3 dissociated systems are also considered. By use of a (001) relaxed Ti2O9H10 cluster, the role of anatase support on SCR reaction is investigated. Since NH2NO formation on Ti2O9H10 cluster requires lower activation barriers than on V2O5 surface, it is proposed that the role of titanium dioxide on SCR reaction could be forming NH2NO. The role of vanadium oxide is crucial in terms of dissociating this product into H2O and N2. Finally, NH3 adsorption is studied on a V2TiO14H14 cluster which represents a model for vanadia/titania surface.
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Tussupbayev, Samat. "Theoretical study of reactivity and dynamics of hybride-bridged diruthenium complexes and silylium." Doctoral thesis, Universitat de Girona, 2009. http://hdl.handle.net/10803/8052.
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Esta tesis presenta un estudio computacional de los sistemas con hidruros puente. En la primera parte se estudia la química de complejos de dirutenio con cuatro hidruros puente. Esto incluye las siguientes reacciones: el intercambio del hidruro con hidrógeno molecular; la activación del enlace C-H del etileno para formar el complejo de bis(vinilo)-etileno; el acoplamiento C-C entre el etileno coordinado y dos ligandos vinilo para producir el complejo rutenaciclopentadieno. Al final de esta parte, se discuten a detalle los mecanismos de estas reacciones. Además, se demostró la importancia de la flexibilidad de los ligandos hidruro y la cooperación entre los dos centros metálicos. En la segunda parte, se estudió el comportamiento fluxional de dos complejos μ-silileno y de un catión sililio. Con esto, se estableció la ruta más favorable en donde se realiza el intercambio de los ligandos hidruro y de los grupos metilo en los complejos μ-silileno. Finalmente, se encontró que hay dos posibles rutas relativas al cambio en la posición del puente Si-H-Si en el cation sililio poliagóstico, asociadas con la rotación interna de los grupos sililo.
The thesis presents a computational study of hydride bridged systems. The chemistry of diruthenium tetrahydride-bridged complex was studied in the first part. It includes the next reactions: the hydride exchange with dihydrogen; the C-H bond activation in ethylene to yield bis(vinyl) ethylene complex; the C-C coupling between coordinated ethy¬lene and two vinyl ligands to yield ruthenacyclopentadiene complex. The detailed mechanism of these reactions has been determined. The importance of flexibility of hydride ligands and cooperation between two metal centers has been demonstrated.
The fluxional behavior of two μ-silylene complexes and a silylium cation was studied in the second part. The pathway responsible for the site-exchange of hydride ligands and methyl groups in the μ-silylene complexes has been established. Two possible mecha¬nisms of the shift of Si-H-Si bridge position in the polyagostic silylium cation, associated with internal rota¬tion of si¬lyl groups have been found.
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Pérez, Gallegos Ayax. "Theoretical study on the mechanism of the reaction catalyzed by protein kinase." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/386487.
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Malgrat el gran nombre d’estudis experimentals i computacionals sobre l’estructura i funció de les proteïnes quinases, els detalls exactes dels canvis estructurals i mecanístics dels passos individuals de la reacció catalítica de transferència del grup fosforil romanen incerts. En principi, els estudis computacionals poden subministrar informació minuciosa i una coneixença complementària al treball experimental, però aquest objectiu només es pot assolir si es fan servir els mètodes computacionals adequats i si el model teòric que s’utilitza representa correctament el sistema biològic.
En aquesta Tesi, el mètode QM/MM a nivell DFT/MM s’ha utilitzat per a descriure els diferents mecanismes de reacció sobre la hipersuperfície d’energia potencial de la reacció global de transferència del grup fosforil catalitzada per la Proteïna Quinasa A (PKA). Cal destacar, que a més d’utilitzar models complets i solvatats del sistema biomolecular i nivells de teoria més alts que en treballs anteriors, s’han fet servir també diferents tècniques i algoritmes inclosos en el codi ChemShell, a fi de millorar els càlculs dels camins de reacció i les optimitzacions d’estats estacionaris. En particular, coordenades de reacció més flexibles i el mètode microiteratiu per a localitzar estructures d’estats de transició ens han permès aplicar una metodologia multiescala consistent i fiable per a analitzar minuciosament tant el mecanisme associatiu (que implica la transferència de fosforil simultàniament amb la protonació del grup fosfat transferit) com el dissociatiu (que implica dues etapes: la transferència de fosforil i la protonació del substrat fosforilat) de la reacció de transferència de fosforil catalitzada per la PKA. S’ha prestat especial atenció a les funcions específiques dels residus Asp166, Lys168 i Thr201, al Gly-rich loop, als ions metàl·lics, i a la conformació i l’estat de protonació al llarg de la reacció química de la cadena lateral del substrat i del fosfat que es transfereix.
Els resultats d’aquesta Tesi han demostrat que la reacció catalitzada per la PKA no depèn del substrat i que el mecanisme dissociatiu és clarament favorable respecte el mecanisme associatiu. No obstant, els càlculs presentats també mostren que el mecanisme associatiu seria viable quan el dissociatiu està impedit, com amb el mutant D166A. Aquest punt reobre un debat sobre la viabilitat del mecanisme associatiu que semblava superat donat els darrers estudis teòrics. A més a més, els camins de reacció per a la retro-protonació del substrat fosforilat per part del residu Asp166 s’han localitzat, demostrant que Asp166 es comporta com un catalitzador àcid/base general al llarg del mecanisme dissociatiu. Per altra banda, els perfils d’energia potencial QM/MM calculats també demostren, per primera vegada, que la reacció catalítica de transferència de fosforil és viable amb ions metàl·lics alcalinoterris diferents del Mg2+, confirmant resultats experimentals recents que proposen el paper fisiològic del Ca2+ a l’activitat de les quinases. Tant pel mecanisme associatiu com pel dissociatiu, la localització precisa i l’orientació de la triada Asp166-Lys168-Thr201 i de la xarxa de ponts d’hidrogen que aquests residus estableixen al centre actiu, s’ha vist que són essencials per a la catàlisi i especialment per a l’estabilització de les estructures dels estats de transició involucrats.
Finalment, els resultats d’aquesta Tesi han proveït amb una seqüència completa de l’evolució geomètrica de l’estructura del complex ternari al llarg de la reacció catalítica. Això permet una comparació acurada amb les estructures de raigs-X cristal·logràfiques que han estat proposades experimentalment com a imatges moleculars del procés catalític de fosforilació. En particular, el bon acord entre les estructures teòriques i els estudis experimentals validen la visió atòmica de la reacció presentada en aquesta Tesi, revelant canvis conformacionals, de coordinació i dels ponts d’hidrogen que tenen lloc durant la recció química i la seva relació amb la dinàmica de l’enzim.Despite extensive experimental and computational studies about the structure and function of kinases, exact details regarding the complex structural changes and the mechanistic details of individual stages involved in the catalyzed phosphoryl-transfer reaction remain uncertain. In principle, computational studies can provide detailed information and insights to complement experimental studies, but this goal can only be attained when the appropriate computational approaches are employed and the theoretical model used is a good mimic of the biological system. In this Thesis, the QM/MM approach at the DFT/MM level of theory was used to describe the different reaction mechanisms on the potential energy hypersurface of the global phosphoryl-transfer reaction catalyzed by the Protein Kinase A (PKA). Remarkably, besides making use of more complete solvated models of the biomolecular system and higher levels of theory than the ones employed in previous works, several techniques and algorithms within the computational chemistry suite ChemShell were used to improve the accuracy of the reaction path calculations and stationary points optimizations. In particular, more flexible reaction coordinates, the location of the stationary points with the hybrid delocalized internal coordinates, and the microiterative method to locate transition structures allowed us to apply a consistent and reliable multiscale methodology to examine minutely both the associative (involving a concomitant phosphoryl-transfer and protonation of transferred phosphate) and dissociative (involving two steps: phosphoryl-transfer and back protonation of the phosphorylated substrate) mechanisms of the phosphoryl-transfer reaction catalyzed by PKA. Special attention was paid in the specific roles of the invariant residues Asp166, Lys168, and Thr201, the conserved Gly-rich loop, the metal ions, and the conformation and protonation state of the substrate residue side chain and transferred phosphate along the chemical reaction. The results in this Thesis demonstrate that the catalytic reaction catalyzed by PKA is not substrate-dependent and that the dissociative mechanism is clearly more favorable than the associative one. Nevertheless, the presented calculations also show the plausibility of the associative reaction pathway when the dissociative counterpart is impeded as it is in the D166A mutant. This reopens the debate about the plausibility of the associative reaction pathway that in view of the last theoretical works in the field seemed to be overcame. Moreover, the reaction paths for the back protonation of the phosphorylated substrate by Asp166 have been located, so demonstrating that Asp166 behaves as a general acid/base catalyst along the dissociative mechanism. In addition, QM/MM potential energy profiles determined in this Thesis also demonstrate, for the first time, that the catalyzed phosphoryl-transfer is plausible with alkali earth metal ions other than Mg2+ ions, what confirms recent experimental results where the physiological role of Ca2+ in kinase activity has been proposed. For both the associative and the dissociative mechanisms, the precise location and orientation of the triad Asp166-Lys168-Thr201 and the hydrogen bond network these residues establish within the active site are shown to be essential for catalysis, particularly in the stabilization of the transition state structures involved. Lastly, the results in this Thesis provide a complete sequence of the geometrical evolution of the structure of the ternary complex along the catalytic reaction. This permits an accurate comparison with new X-ray crystallographic structures that have been suggested as experimental snapshots of the catalyzed-phosphorylation process In particular, the good agreement between the theoretically determined structures and the crystallographic studies validate the atomic view of the reaction presented in this Thesis, thus revealing conformational, coordination, and hydrogen bond changes that occur during the chemical step and its relation with the enzyme dynamics.
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Naber, Christoph [Verfasser], Jürgen [Akademischer Betreuer] Neubauer, and Jürgen [Gutachter] Neubauer. "Hydration kinetics of tricalcium silicate: A dataset for reaction rate calculations and nanoscale analysis employing atom probe tomography / Christoph Naber ; Gutachter: Jürgen Neubauer ; Betreuer: Jürgen Neubauer." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2019. http://d-nb.info/1176809806/34.
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Fischer, Gerd. "Quantenchemische Berechnungen zur enantioselektiv katalysierten Aldolreaktion." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1089129893015-50097.
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Die Mukaiyama-Aldolreaktion ist die Umsetzung eines Silylenolethers mit einer Carbonylverbindung in Gegenwart einer Lewis-Säure. Diese Reaktion ist eine wichtige Methode zur Knüpfung einer Kohlenstoff-Kohlenstoff-Bindung in der Organischen Chemie. In der vorliegenden Arbeit wird mittels quantenchemischer Methoden ein Einblick in den Mechanismus der Reaktion und die Ursachen der Enantioselektivität gegeben. Ausgehend von der unkatalysierten Reaktion wurde der Mechanismus der von kleineren achiralen Lewis-Säuren wie BF3 und TiCl4 katalysierten bzw. vermittelten Reaktion bearbeitet. Mit dem NEB-Verfahren zur Berechnung des Reaktionsmechanismus der enantioselektiv katalysierten Reaktion kam eine neuartige Möglichkeit zur Optimierung von Reaktionswegen zum Einsatz. Es konnte gezeigt werden, dass die Optimierung auch sehr komplexer Reaktionswege möglich ist. So wurde der gesamte katalytische Cyclus der Ti-BINOL katalysierten Reaktion berechnet, wobei sich der Einsatz der DFTB-Methode (density-functional based tight-binding method) zur Berechnung des Systems als sehr gut geeignet erwies. Die Leistungsfähigkeit der DFTB Methode konnte im Vergleich mit den geometrischen Daten aus Röntgenkristallstrukturanalysen nachgewiesen werden. Die Richtung der stereochemischen Differenzierung konnte in Übereinstimmung mit den experimentellen Ergebnissen bestimmt werden. Aus diesem Ergebnis war es möglich, ein schematisches Modell zu entwickeln, das die Ursache der Selektivität veranschaulicht.
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Patwardhan, Neeraj Narendra. "Study of Synthesis, Reactions and Enantiomerization of Cα-Chiral Grignard Reagents." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/37814.
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The development of chiral organometallics for asymmetric synthesis is a topic of significant research in the recent past. The most studied in this class are the chiral organolithium reagents with many reported examples. The primary focus of our research is the development of Cα-chiral Grignard reagents, where the metal bearing α-carbon is the sole source of chirality. Examples of such Grignard reagents are rare owing to the problems associated with their synthesis, and their low configurational stability. We have studied these problems in three different modules of this project.
Reactions of 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile with carbon electrophiles are first attempted in order to expand the utility of this configurationally stable Cα-chiral Grignard reagent in asymmetric synthesis. This reagent has been shown to be non-reactive towards carbon electrophiles at low temperatures. Consequently, we attempt to enhance the reactivity of this compound through two different approaches, Lewis-base activation and the "ate-complex" generation. The Magnesium/Halogen (Mg/X) exchange reactions have been shown to be extremely useful in the synthesis of complex Aryl, alkenyl (sp²) and alkynyl (sp) Grignard reagents. Examples of Mg/X exchange reactions of Alkyl (sp³) halides are, however, rare. Even more rare are such examples with secondary and tertiary alkyl halides, justifying the relative paucity of chiral Grignard reagents. In this module of our project, we study the Mg/X exchange reactions on secondary alkyl halides possessing a γ-hydroxyl group, as an internal activator for such Mg/X exchange reactions.
Enantiomerization pathways of chiral organolithium compounds have been widely studied. However, few such studies have been performed on chiral Grignard reagents. In this module of the project, we studied the solvent assisted enantiomerization mechanism of the Cα-chiral 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile. Rate constant for the enantiomerization of this compound was measured in three different ethereal solvents to study the effect of solvent on the configurational stability. Finally, the order of the enantiomerization process with respect to [Et₂O] was studied in order to predict the mechanism of this process in Et₂O solvent.
Our kinetic studies on the enantiomerization process provided us with a definitive picture for the enantiomerization of the Cα-chiral 1-magnesio-2,2-diphenyl-cyclopropylcarbonitrile, where solvation of the Grignard reagent preceded an ion-pair separation step which eventually lead to enantiomerization of the Grignard species. However, the precise structure of all the involved solvated intermediates could not be determined as kinetics was not able to distinguish between these intermediates. We next performed computational calculations to study the effect of solvation on the analogous 1-magnesio-cyclopropylcarbonitrile in order to address the unanswered questions from our kinetic studies.Ph. D.
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Kumbhani, Sambhav Rajendra. "Peroxy Radical - Water Complexes: Their Role in the Atmosphere." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5729.
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The importance of radical-water complexes in the atmosphere is explored in this dissertation. Radicals, although present in small concentrations in the atmosphere, play a significant role in creating and removing atmospheric pollution. As the atmosphere warms and consequently gets wetter, it is essential to understand the effects of water vapor on radical chemistry. This dissertation reports studies on the effects of water vapor on the kinetics of the self-reaction of β-hydroxyethyl peroxy radical (β-HEP), a prominent organic peroxy radical in the atmosphere. Both experimental and computational studies have been performed to examine the effects of water vapor on the kinetics of the self-reaction. The influence of water vapor and temperature on the reaction rate constant is presented. The rate of the self-reaction increases between 2 to 6 times with an increase in water vapor and decrease in temperature. The products of the self-reaction in the presence and absence of water vapor have been computed using high level ab initio calculations. Major products include alkoxy radicals, peroxides, aldehydes, alcohols and oxygen. A new reaction pathway leading to formation of hydroperoxy radical (HO2) from the self-reaction of β-HEP in the presence of water vapor was identified. In the presence of high NOx concentration HO2, forms tropospheric ozone, which is classified as a harmful pollutant by the Environmental Protection Agency (EPA). Like tropospheric ozone, aerosols are also classified as harmful pollutants by the EPA. Sulfuric acid-water complexes are estimated to be the primary reason for new aerosol formation in the atmosphere. However, the sulfuric acid concentration in the atmosphere alone is not sufficient to account for observed aerosol concentrations. Classical nucleation theory is used to explain new particle formation (NPF), which is initiated by the formation of a nucleating site (a highly polar complex). This dissertation explores the role of various radical-molecule complexes acting as the nucleating site. Experimentally, the HO2-water complex is studied as a possible nucleating site for NPF. A new instrument was developed to create and measure radical-water complex initiated particle formation. The instrument incorporates two scanning mobility particle sizers (SMPS) to measure the size distribution and number density of the aerosol particles formed. The experimental setup uses UV absorption spectroscopy and wavelength modulated spectroscopy to measurethe HO2 radical and water vapor concentrations in the reaction cell. No significant particle formation was observed at room temperature and pressure. Particle formation from the HO2-water complex, may occur at lower temperatures. Additional radical-molecule complexes have been studied computationally in an effort to identify other possible nucleating sites for particle formation. In particular, the complexes of sulfuric acid, nitric acid, acetic acid and formic acid with ammonia, amidogen radical (NH2) and imidogen radical (NH) have been studied. H2SO4-NH2 and HNO3-NH2 complexes show the potential to act as nucleating sites for formation of aerosol particles in the atmosphere. In summary, water mediated chemistry plays a significant role in the atmosphere and must be included in scientific models to better predict pollution levels in the atmosphere.
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Souza, Luiz Augusto Gesteira de. "Cálculos usando métodos de estrutura eletrônica na obtenção de parâmetros cinéticos e termoquímicos." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/46/46132/tde-08022018-090432/.
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Cálculos usando métodos de estrutura eletrônica (Hartree-Fock, Mõller-Plesset de segunda ordem e DFT, B3LYP) foram efetuados pelo programa Gaussian98 em microcomputadores e estações de trabalho, com o objetivo de elucidar os canais de decomposição unimolecular de éter dietílico em fase gasosa e foram comparados com valores obtidos através de aproximações baseadas na mecânica estatística pela metodologia de Benson. O éter dietílico vem sendo usado como um aditivo para o óleo diesel e combustível alternativo e o conhecimento de suas vias vias de decomposição é fundamental nestas investigações. Dezesseis modos primários, do qual, quatro ocorrem através de cisão de ligações simples C-O, C-C,C(1)-H e C(2)-H e doze ocorrendo através de estados de transição cíclicos, os quais eliminam produtos como hidrogênio etano, acetaldeído, etano, álcool etílico, metil etil éter, metano, alguns carbenos e também di-radicais, foram considerados para a determinação das barreiras de ativação, entalpias de reação, entropias de reação e energia livre de Gibbs de reação. Vias primárias ocorrendo através de cisão de ligação, não reproduziram os valores experimentais para as barreiras de ativação, mas reproduziram de modo significante, valores da entalpia da reação. Eliminação de eteno e álcool etílico, ocorrendo através de um estado de transição de quatro centros, apresentou a barreira de ativação mais baixa. Acetaldeído e eliminação de etano, ocorrendo através de quatro centros, apresentou barreira significativamente alta, mas por outro lado, a menor entalpia, ligeiramente exotérmica por -0,8 kcal.mol-1. Eliminações 1,2 de metano e carbeno ocorrendo através de três centros, junto com a eliminação 1, 1 de hidrogênio e carbeno por três centros, eliminação 2,2 hidrogênio e carbeno por três centros e eliminação 1,4 de hidrogênio, acetaldeído e eteno por seis centros, apresentaram barreiras de ativação relativamente próximas mostrando que elas são competitivas entre si. Os valores computados dos canais que ocorrem por estados de transição cíclicos foram comparados com os resultados experimentais disponíveis e discutida a validade desta abordagem computacional para o estudo de reações unimoleculares de multi-canais. Determinação de parâmetros termoquímicos, como calor de formação para espécies radicalares dos canais de decomposição primário e alguns radicais alcóxidos, junto com a estimativa de afinidade eletrônica e protônica (com a abordagem ab initio Gaussian 2 a qual estima energias eletrônicas muito precisas) foram efetuados e seus resultados foram comparados com os valores experimentais disponíveis e valores obtidos através de energias de ligação e da regra de aditividade de Benson.Calculations using methods of electronic structure(Hartree-Fock, second order Moller-Plesset and DFT: B3LYP) had been effected through the Gaussian98 program in microcomputers and workstations, with the objective to elucidate the unimolecular decomposition channels of diethyl ether in gaseous phase. These results also had been compared to those obtained by the methodology based in statistical mechanics through Benson\'s approach. Sixteen primary ways, which, four occur through the break of simple bonds C-O, C-C,C(1)-H, C(2)-H, and twelve occur through cyclical transistion states, which eliminate products as hydrogen, ethene, acetaldehyde, ethane, ethyl alcohol, methyl ethyl ether, methane, some carbenes and also diradicals. These products had been considered to the determination of the activation barriers, enthalpies of reaction, entropies of reaction and free energy of Gibbs of reaction. Primary ways occurring through the break of bonds, had not reproduced experimental values for the activation barriers, however they had reproduced in a significant way, values of the enthalpy of the reaction. Elimination of ethene and ethyl alcohol, occurring by a transition state of four centers, presented the lowest activation barrier. Acetaldehyde and ethane elimination occurring through four centers, presented a high significantly barrier, but on the other hand it presented the smallest enthalpy, lightly exothermic above -0,8 kcal.mol-1. Eliminations 1,2 of methane and carbene occurring through three centers, together with the elimination 1,1 of hydrogen and carbene through three centers, elimination 2,2 of hydrogen and carbene through three centers and elimination 1,4 of hydrogen, acetaldehyde and ethene through six centers, had presented relatively next activation barriers, showing that they are competitive among themselves. The computed values of the channels that occur through cyclical transition states had been compared with the available experimental results and the trustworthiness of this computational boarding for the study of unimolecular reactions in multi-channel had been dicussed. Determination of thermochemical parameters, as heat of formation for radicalar species of the primary channel of decomposition and some alcoxyde radicais, together with the estimative of the electronic and protonic affinities,( with the ab initio Gaussian 2 boarding which estimate very precise eletronic energies ) and their results had been compared with the available experimental values and with values gotten through energies of bond and Benson\'s additivity rule.
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Larina, Nina. "3-(2-Benzylbenzoyl)-4(1H)-quinolinones : une nouvelle classe de composés photochromiques photoréversibles." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22110/document.
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Actuellement, les photochromes photoréversibles présentent un intérêt important en vue de leurs applications éventuelles comme interrupteurs optiques ou pour le traitement et le stockage de données. L’objectif principal de ce travail de thèse a été d’évaluer les 3--(2--benzylbenzoyl)--4--quinolones en tant que système photochromique photoréversible. Afin d’étudier la relation entre la structure chimique et le comportement photochromique de ce système, une série de nouvelles 3--(2--benzylbenzoyl)--4--quinolones à substitution variée a été préparée à l’aide de procédures connues ainsi qu’élaborées lors de ce travail. La photoréaction de ces nouveaux molecules étant très complexe, une méthode d’étude a été établie avec des 2--benzyl--3--benzoyl--4--quinolones photoénolisables au comportement plus simple. Leurs spectres d’absorption modélisés à l’aide de fonctions pekariennes ont été comparés avec les résultats des calculs quantiques. Le mécanisme selon lequel la réaction de décoloration se fait par l’ionisation des photoénols fortement acides via protonation des molécules du solvant a été établi. Enfin, la troisième partie est consacrée à l’étude des nouveaux dérivés de quinolones. D’après l’analyse de leurs spectres d’absorption, ainsi que les résultats des calculs quantiques, nous proposons un mécanisme où le transfert d’hydrogène photo--induit conduirait à la formation d’un intermédiaire biradicalaire, capable de se cycliser en dibenzo[b]acrydinones hydroxysubstituées. Un tel mécanisme expliquerait la forte influence qu’ont la nature des substituants en positions 1 et 2, ainsi que la température et la présence d’oxygène sur la régio-- et stéréo--sélectivité de cette photoréactionPhotoreversible photochromic compounds are currently of considerable interest from the point of view of their potential applications as molecular switches and for data storage and processing. The main target of the present investigation is to evaluate the scope and limitations of 3--(2--benzylbenzoyl)--4--quinolones as a photoreversible photochromic system. In order to investigate the relationship between quinolone chemical structures and photochemical behavior, a large series of new 3--(2--benzylbenzoyl)--4--quinolones with different substituents has been prepared using known as well as newly elaborated synthetic procedures. In the second part of the work a series of simpler photoenolizable 2--benzyl--3--benzoyl quinolones is studied by the means of fitting their UV--Vis absorption spectra and comparison with the results of quantum mechanical calculations at the TD DFT level. It was concluded that the mechanism of the reverse reaction involves ionization of the strongly acidic photoenols via protonation of the solvent molecules. The third part of the work includes investigation of the new quinolone derivatives. From the analyses of their absorption spectra and the results of quantum mechanical calculations, we propose a tentative mechanism, according to which the photoinduced hydrogen transfer yields a biradical, capable of cyclization into the hydroxy substituted dibenzo[b]acrydinones. This mechanism accounts for the observation that the nature of substituents in positions 1 and 2, the temperature and the presence of oxygen strongly affect regio-- and stereoselectivity of the cyclization
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Fernández, Alvarez Víctor Miguel. "A computational approach to the mechanism of light-driven reactions in solution." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/402464.
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Aquesta tesi doctoral descriu l'aplicació, d'una combinació de mètodes DFT (Teoria del Funcional de la Densitat) i models cinètics, per elucidar el mecanisme de reaccions en solució iniciades per llum. Aquesta estratègia és usada per estudiar dos tipus de reaccions d'interès comercial. A la primera part, s'analitza el mecanisme de transformacions químiques activades directament per llum. En canvi, la segona part abasta reaccions en què l'activació lumínica passa a través d'un foto-catalitzador. En tots dos casos, els resultats i les propietats experimentals, com ara la selectivitat o el rendiment quàntic, van ser reeixidament reproduïts, i racionalitzats d'acord a les propietats d'estructura electrònica que defineixen els sistemes involucrats. A més, es va demostrar que els models cinètics són crucials per calcular aspectes del mecanisme de transformacions foto-induïdes, ja que la mera comparació de barreres d'energia no té en compte les grans diferències de concentracions presents.Esta tesis doctoral describe la aplicación, de una combinación de métodos DFT (Teoría del Funcional de la Densidad) y modelos cinéticos, para elucidar el mecanismo de reacciones en solución iniciadas por luz. Esta estrategia es usada para estudiar dos tipos de reacciones de interés comercial. En la primera parte, se analiza el mecanismo de transformaciones químicas activadas directamente por luz. En cambio, la segunda parte abarca reacciones en las que la activación lumínica ocurre a través de un foto-catalizador. En ambos casos, los resultados y las propiedades experimentales, tales como la selectividad o el rendimiento cuántico, fueron exitosamente reproducidos, y racionalizados de acuerdo a las propiedades de estructura electrónica que definen a los sistemas involucrados. Además, se demostró que los modelos cinéticos son cruciales para calcular aspectos del mecanismo de transformaciones foto-inducidas, ya que la mera comparación de barreras de energía no tiene en cuenta las grandes diferencias de concentraciones presentes.
This doctoral thesis describes the application of a combination of Density Functional Theory (DFT) methods and kinetic models to elucidate the mechanism of light-driven synthesis reactions in solution. This strategy is applied to study two types of reactions of commercial interest. In the first part, the mechanism of chemical transformations directly activated by visible light is analyzed. On the other hand, the second part covers reactions in which light activation takes place via a photocatalyst. For both cases, experimental outcomes and properties such as selectivity and quantum yield were correctly reproduced and rationalized on the basis of the electronic structure properties that define the systems involved. In addition, kinetic models proved vital in the computation of mechanistic aspects of photo-induced transformations as mere comparisons of energy barriers fail to account for large differences in concentration present.
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Akhtar, Shamim. "Study of the 12C(α,γ)16O Reaction via the α-Transfer Reactions: 12C(6Li,d)16O and 12C(7Li,t)16O." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1471384669.
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Chen, Szu-Lin. "An empirical potential for hydrogen bond energies determination of the orientation of anthracene molecules in the unit cell by means of a refractivity method: some ab initio calculations involving acetonitrile exchange reaction." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76509.
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Topic I
An empirical potential for calculating hydrogen bonding energies is developed for systems of the type A-H--B, where A and/or B is oxygen or nitrogen. Point charge and van der Waals interaction are included in the potential. The parameters of the potential were optimized by means of a simplex algorithm within a range of A-B distances from 2.8 A through 5.0 A. The root mean square deviation between the empirical potential and the ab initio results of 216 configurations of (H₂O)₂, (NH₃)₂ and NH₃•H₂O is 0.9 kcal/mol and 0.5 kcal/mol for 61 configurations of methanol dimers. Applications of the potential to water dimers, ammonia dimers, their mixed dimers, water oligomers and ice-h as well as the β form of the methanol crystal show that the potential yields reasonable results compared to those computed by "ab initio" methods using 6-31G* basis sets. The potential is compatible with MM2 program. It is simpler than earlier potentials in that neither dipoles nor Morse potentials are involved. It should be superior to the empirical potentials developed by Jorgensen that used STO-3G ab initio calculated results as the standards. The potential might be useful for estimation of hydrogen bond energies in a local part of a large molecule to avoid the prohibitive expense of ab initio calculation.
Topic II
The monoclinic anthracene crystal is used as an example to demonstrate the feasibility of optimizing the orientation of molecules in the unit cell by matching calculated and experimental refractivity ellipsoids using a simplex algorithm. The calculated refractivity ellipsoid is determined by use of an empirical formula using bond directional polarizabilities. Optimization of the molecular orientations to provide the best fit to the experimental ellipsoid starting from several assumed orientations results in fits for which the maximum deviation from the experimental molecular orientation was no more than 10 degrees. The method can be applied to other monoclinic molecular crystals directly and could be extended to other crystal systems with anisotropic optical properties.
Topic III
Three mechanisms (Walden inversion, addition-rearrangement-elimination and proton 1,3 shift mechanisms) of the following reaction were suggested by Jay et al. and Andrade et al. respectively.
CH₃CN + C⃰N- = CH₃C⃰N + CN-.
The mechanism of Walden inversion was determined to be the least likely one based on Andrade's MNDO results. Our calculations, based on 3-21G and 4-31G results, show the contrary result that the Walden inversion is the most likely mechanism among the three considered. However, solvation effects were neglected in the calculations and these effects could play a major role in the choice of mechanisms. Simple calculations based on Boltzmann distribution of precursor concentrations and the Arrhenius law show that Walden inversion predominates over Jay's addition-elimination-rearrangement mechanism even when MNDO energy levels were used. Estimated orders of magnitude for the rate ratios were determined.Ph. D.
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Remmert, Sarah M. "Reduced dimensionality quantum dynamics of chemical reactions." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:7f96405f-105c-4ca3-9b8a-06f77d84606a.
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In this thesis a reduced dimensionality quantum scattering model is applied to the study of polyatomic reactions of type X + CH4 <--> XH + CH3. Two dimensional quantum scattering of the symmetric hydrogen exchange reaction CH3+CH4 <--> CH4+CH3 is performed on an 18-parameter double-Morse analytical function derived from ab initio calculations at the CCSD(T)/cc-pVTZ//MP2/cc-pVTZ level of theory. Spectator mode motion is approximately treated via inclusion of curvilinear or rectilinear projected zero-point energies in the potential surface. The close-coupled equations are solved using R-matrix propagation. The state-to-state probabilities and integral and differential cross sections show the reaction to be primarily vibrationally adiabatic and backwards scattered. Quantum properties such as heavy-light-heavy oscillating reactivity and resonance features significantly influence the reaction dynamics. Deuterium substitution at the primary site is the dominant kinetic isotope effect. Thermal rate constants are in excellent agreement with experiment. The method is also applied to the study of electronically nonadiabatic transitions in the CH3 + HCl <--> CH4 + Cl(2PJ) reaction. Electrovibrational basis sets are used to construct the close-coupled equations, which are solved via Rmatrix propagation using a system of three potential energy surfaces coupled by spin-orbit interaction. Ground and excited electronic surfaces are developed using a 29-parameter double-Morse function with ab initio data at the CCSD(T)/ccpV( Q+d)Z-dk//MP2/cc-pV(T+d)Z-dk level of theory, and with basis set extrapolated data, both corrected via curvilinear projected spectator zero-point energies. Coupling surfaces are developed by fitting MCSCF/cc-pV(T+d)Z-dk ab initio spin orbit constants to 8-parameter functions. Scattering calculations are performed for the ground adiabatic and coupled surface models, and reaction probabilities, thermal rate constants and integral and differential cross sections are presented. Thermal rate constants on the basis set extrapolated surface are in excellent agreement with experiment. Characterisation of electronically nonadiabatic nonreactive and reactive transitions indicate the close correlation between vibrational excitation and nonadiabatic transition. A model for comparing the nonadiabatic cross section branching ratio to experiment is discussed.
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Russell, Caroline. "Quantum mechanical wavepacket calculations on chemical reactions." Thesis, University of Oxford, 1998. https://ora.ox.ac.uk/objects/uuid:bc8fa8c2-7fbd-4fb4-bddf-8086442e36b7.
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The quantum mechanical time-dependent wavepacket method is introduced in the context of the field of chemical dynamics. The theory of the method is presented for two processes of interest in dynamics: molecular photodissociation, and reactive scattering. For the first of these processes, an expression is derived for the absorption spectrum of a molecule undergoing an electronic bound-continuum transition. For the second process, a time-dependent formulation is obtained for the S-matrix, and the "flux formulation" for the calculation of initial state-selected reaction probabilities (ISSRPs) is shown to be equivalent to summing over appropriate S-matrix elements. The time-dependent wavepacket theory for molecular photodissociation is used in the calculation of the photodetachment spectrum of the FHÌ
â anion. Spectra are calculated for two different energy resolutions, and previously unobserved structure is seen in the higher resolution spectrum. The structure is assigned by studying energy-dependent wavefunctions corresponding to each peak in the spectrum. Some peaks are assigned to direct scattering states, while others are assigned to quantum mechanical resonance states localised in the reactant and product valleys of the potential energy surface. The implication of this is that a high-resolution photodetachment experiment may provide the first experimental evidence for resonances in the F + H2 reaction. For reactive scattering, the time-dependent wavepacket method is used (in conjunction with the rotationally adiabatic approximation for J > 0 calculations) to calculate ISSRPs for various initial states of the nearly-thermoneutral ionmolecule reaction: N+(3P)+H2(1Σ+g)âNH+(X2II)+H(2S). Dense resonance structure in the reaction probabilities for J = 0 is attributed to the influence of the deep wells in. the potential energy surface for the reaction. The ISSRPs are used to calculate initial state-selected cross sections and rate constants which are compared with the results of some earlier trajectory calculations and with experimental data. The implications of the results for the astrophysical significance of the reaction are discussed.
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Griffith, Kent Joseph. "Atomic and electronic structure of complex metal oxides during electrochemical reaction with lithium." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271191.
Full textAbstract:
Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.
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Leite, Daniel Fujimura. "Estudo teórico/experimental comparativo do catalisador brometo de 1-propil-4-azo-1-azôniobiciclo[2,2,2]octano (P-DABCO) para a ciclo-adição catalítica de CO2 aos epóxidos para a formação de ciclocarbonatos orgânicos." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-21092015-082950/.
Full textAbstract:
Com o aumento da consciência global sobre os riscos do Aquecimento do Planeta e de suas possíveis causas ficou claro que é necessário desenvolver ou adaptar processos industriais de maneira a aproveitar dejetos como o CO2. Dentre as formas de se aproveitar o CO2, destaca-se a ciclo-adição aos epóxidos, com a formação de ciclocarbonatos. A reação é tecnologicamente interessante, pois ciclocarbonatos possuem diversas aplicações como solventes polares apróticos, eletrólitos e matéria prima para compostos como purinas, carbamatos, glicóis, policarbonato e outros. Para que a reação ocorra em tempo e condições viáveis, há a necessidade de se trabalhar com catalisadores. Foram reportados muitos catalisadores ao longo dos anos. Dentre os catalisadores mais comumente utilizados, destacam-se os sais orgânicos. Porém o estudo sobre modelos cinéticos e mecanismo de reação ainda carecem de mais atenção. Desta forma este trabalho propõe-se a estudar esta parte, através de experimentos cinéticos, modelos teóricos e cálculos de química quântica. Para isto escolheu-se estudar a ação catalítica do brometo de 1-propil-4-azo-1-azôniobiciclo[2,2,2]octano (P-DABCO) frente a um catalisador bem descrito na literatura, o brometo de tetrapropilamônio (TPA).Nowadays mankind are becoming more aware about Global Warming risks and its possible causes. With that in mind, it is necessary to develop or to adapt industrial processes to use some wastes like CO2. One of the best strategies to utilize CO2 is to convert it to cyclic carbonate through cyclic addition reaction to epoxides. This reaction is important because cyclic carbonates have other useful applications. For example, they can be used as polar aprotic solvents, electrolytes and as starting material for other compounds like purine, carbamates, glycols, polycarbonate, among others. However, the cyclic addition reaction must be catalyzed so as to get the desired product in short possible time and under soft conditions. Many catalysts have been reported in the literature that can be used for the cyclic addition reaction, with the organic salts being very common ones. Most of these reports focus on the efficiency of the catalyst and little attention has been paid to the reaction kinetics models and reaction mechanisms. Thus, we intend to study this part. For this purpose, we will do kinetics experiments, theoretical models and quantum chemistry calculation. The 1-alkyl-4-aza-1-azaniabicyclo[2.2.2]octyl bromide was chosen to this work and will be compared with tetrapropylammonium bromide that is known in the literature.
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Pavelka, Radomil. "Pohon vřeten pětivřetenového soustružnického automatu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231522.
Full textAbstract:
The subject of the thesis is design of independent spindle drive for multi-spindle automatic lathe MORI-SAY TMZ 520 CNC manufactured by TAJMAC-ZPS. The thesis will introduce the representatives of manufacturing program of TAJMAC-ZPS multi-spindle automatic lathes division and there will be a brief description of their main constructional parts. The main objective of the thesis is an engineering design of testing device which will be bulit for verification of the correct drive concept. There is also many calculations and detailed description of the engineering design. The testing device is made for internal needs of TAJMAC-ZPS.
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Field, G. M. "Pre-equilibrium processes in nuclear reactions." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233509.
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Tuttelberg, Kaur. "STORM in Monte Carlo reactor physics calculations." Thesis, KTH, Fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146284.
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RIBEIRO, MARCOS S. "Sistema calorimétrico e software para análise da polimerização de compostos de metacrilato de metila, pela variação da exotermia da reação." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10583.
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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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MURA, LUIS F. L. "Medidas de taxas de reacao nuclear e de indices espectrais ao longo do raio das pastilhas combustiveis do reator IPEN/MB-01." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9617.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Harper, Sterling (Sterling M. ). "Calculating reaction rate derivatives in Monte Carlo neutron transport/." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/106690.
Full textAbstract:
Thesis: S.M. and S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 63-64).
An operating nuclear power reactor is a complex system that is sensitive to many material parameters including densities, temperatures, and compositions. There is great interest in solving the neutron transport with Monte Carlo methods due to their extremely high fidelity, but Monte Carlo methods are too slow to run in an iterative brute-force search of the reactor parameter space. This thesis discusses the derivation, implementation, and applications of differential tallying -- a method which can be used to mitigate the computational cost of mapping out a reactor parameter space with Monte Carlo. With differential tallies, each calculation provides derivatives of tallied quantities like reactivity and fission reaction rates with respect to material density, temperature, etc. These derivatives directly provide reactivity coefficients and they can also be used to extrapolate and predict small changes in reactor parameters. Notably, a novel method is presented which uses the windowed multipole cross section representation to compute temperature derivatives due to the resolved resonance Doppler broadening effect. To demonstrate the utility of differential tallies, this thesis presents example computations of moderator density and fuel Doppler feedback coefficients in pressurized water reactor pincells. With differential tallies, the moderator and fuel Doppler coefficients can be computed 40% and 50x faster, respectively, than by brute-force methods. A calculation of pin-by-pin Doppler coefficients in an assembly is also presented in order to demonstrate that differential tallies are even more efficient for assembly calculations.
by Sterling Harper.
S.M. and S.B.
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Bielawski, Marcin. "Diaryliodonium Salts : Development of Synthetic Methodologies and α-Arylation of Enolates." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-54738.
Full textAbstract:
This thesis describes novel reaction protocols for the synthesis of diaryliodonium salts and also provides an insight to the mechanism of α-arylation of carbonyl compounds with diaryliodonium salts. The first chapter gives a general introduction to the field of hypervalent iodine chemistry, mainly focusing on recent developments and applications of diaryliodonium salts. Chapter two describes the synthesis of electron-rich to electron-poor diaryliodonium triflates, in moderate to excellent yields from a range of arenes and iodoarenes. In chapter three, it is described that molecular iodine can be used together with arenes in a direct one-pot, three-step synthesis of symmetric diaryliodonium triflates. A large scale synthesis of bis(4-tert-butylphenyl)iodonium triflate is also described, controlled and verified by an external research group, further demonstrating the reliability of this methodology. The fourth chapter describes the development of a sequential one-pot synthesis of diaryliodonium salts from aryl iodides and boronic acids, furnishing symmetric and unsymmetric, electron-rich to electron-poor diaryliodonium tetrafluoroborates in moderate to excellent yields. This method was developed to overcome the regiochemical limitations imposed by the reaction mechanism in the protocols described in the preceding chapters. Chapter five describes a one-pot synthesis of heteroaromatic iodonium salts under similar conditions described in chapter two. The final chapter describes the reaction of enolates with chiral diaryliodonium salts or together with a phase transfer catalyst yielding racemic products. DFT calculations were performed, which revealed a low lying energy transition state (TS) between intermediates, which is believed to be responsible for the lack of selectivity observed in the experimental work. It is also proposed that a [2,3] rearrangement is preferred over a [1,2] rearrangement in the α-arylation of carbonyl compounds. The synthetic methodology described in this thesis is the most generally applicable, efficient and high-yielding to date for the synthesis of diaryliodonium salts, making these reagents readily available for various applications in synthesis.
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Chang, Kai-Chin. "Investigation of higher fullerenes." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16700.
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Trifluoromethylierung von Mischungen hoeherer Fullerene mit CF3I wurde in Ampullen bei 400-420 Grad Celsius und 500-600 Grad Celsius durchgefuehrt. Die Produktmischungen wurden mittels mehrstufiger HPLC getrennt. In mehreren Versuchen konnten aus den isolierten HPLC-Fraktionen Kristalle fuer die Roentgenstrukturanalyse gewonnen werden. Die folgenden Strukturen der CF3-Derivate der Fullerene C84, C86 und C88 wurden bestimmt: 1 Isomer von C84(4)(CF3)12, C84(11)(CF3)10, C84(11)(CF3)12, C84(11)(CF3)16, C84(16)(CF3)8, C84(16)(CF3)14, C84(18)(CF3)10, C84(18)(CF3)12, C84(22)(CF3)20, C84(23)(CF3)8, C84(22)(CF3)10, C84(22)(CF3)12, C84(22)(CF3)18, C86(17)(CF3)10, C86(17)(CF3)16, C88(33)(CF3)16, C88(33)(CF3)18 und C88(33)(CF3)20. 2 Isomere von C84(22)(CF3)12, C84(22)(CF3)14 und C84(23)(CF3)14. 3 Isomere von C84(11)(CF3)14. 4 Isomere von C84(22)(CF3)16. Die Additionsmuster der Strukturen wurden diskutiert. Die experimentell nachgewiesenen Strukturen wurden mit berechneten Modellstrukturen verglichen. Dabei wurde auch die Stabilitaet der experimentellen Strukturen vorausgesagt. Zusaetzlich wurden die moeglichen Reaktionspfade fuer die Bildung hoeherer Derivate ausgehend von niedrigen Derivaten diskutiert. Sie zeigen, dass die Regioselektivitaet der Addition vom Kaefigisomer abhaengig ist. Die Reaktionspfade von vier Fullerenkaefigen werden in dieser Arbeit vorgestellt. C84(11)(CF3)10 --> C84(11)(CF3)16 C84(22)(CF3)2 --> C84(22)(CF3)20 C84(23)(CF3)10 --> C84(23)(CF3)18 C86(17)(CF3)10 --> C86(17)(CF3)16Trifluoromethylation of higher fullerene mixtures with CF3I was performed in ampoules at 400 to 420 degree Celsius and 500 to 600 degree Celsius. The obtained product mixtures were separated by multistep HPLC. Subsequent crystal growth and X-ray diffraction measurements allowed for structural characterization of the CF3 derivatives of fullerenes C84, C86 and C88 listed as the following. 1 isomer of C84(4)(CF3)12, C84(11)(CF3)10, C84(11)(CF3)12, C84(11)(CF3)16, C84(16)(CF3)8, C84(16)(CF3)14, C84(18)(CF3)10, C84(18)(CF3)12, C84(22)(CF3)20, C84(23)(CF3)8, C84(22)(CF3)10, C84(22)(CF3)12, C84(22)(CF3)18, C86(17)(CF3)10, C86(17)(CF3)16, C88(33)(CF3)16, C88(33)(CF3)18 and C88(33)(CF3)20. 2 isomers of C84(22)(CF3)12, C84(22)(CF3)14 and C84(23)(CF3)14. 3 isomers of C84(11)(CF3)14. 4 isomers of C84(22)(CF3)16. The molecular structures of isolated isomers were discussed in terms of their addition patterns and relative formation energies. DFT calculations were used to predict stable molecular structures of the CF3 derivatives. Calculated model structures have been compared with the experimental ones. In addition, the reaction pathways from the lower derivatives to higher ones of selected compounds were predicted. The pathways indicate the regioselectivity of additions depending on the fullerene cage isomer. Reaction pathways are presented for four fullerene cages in this work. C84(11)(CF3)10 --> C84(11)(CF3)16 C84(22)(CF3)2 --> C84(22)(CF3)20 C84(23)(CF3)10 --> C84(23)(CF3)18 C86(17)(CF3)10 --> C86(17)(CF3)16
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Hankel, Marlies. "Time-dependent wavepacket methods for the calculation of state-to-state molecular reactive cross sections." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391180.
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Galia, Antonio. "A Dynamic Homogenization Method for Nuclear Reactor Core Calculations." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP042.
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Dans les calculs de réacteurs à trois dimensions, nombreuses techniques d'homogénéisation ont été développées pour l'utilisation du schéma de calcul classique à deux étapes, basé sur les sections efficaces homogénéisées au préalable et utilisées ensuite par interpolation pour un état physique donné.D'autre part, les schémas de calcul basées principalement sur les méthodes des caractéristiques, qui visent le calcul direct du réacteur sans homogénéisation, ont des performances encore limitées en raison des capacités des machines et font alors le recours à des solutions de transport simplifiées. Ce travail a pour objectif d'étudier une nouvelle approche dans laquelle l'homogénéisation dynamique est utilisée pourproduire le flux neutronique de pondération sur les modèles d'assemblage tridimensionnels. L'application de la méthode pour un calcul d'un REP en 3D est comparée aux résultats issus d'un calcul de référence numérique en transport 3D et d'un calcul classique à deux-étapes. La réalisation repose sur le calcul de haute performance et avec un haut niveau de parallélismeThree-dimensional deterministic core calculations are typically based on the classical two-step approach, where the homogenized cross sections of an assembly type are pre-calculated and then interpolated to the actual state in the reactor. The weighting flux used for cross-section homogenization is determined assuming the fundamental mode condition and using a critical-leakage modelthat does not account for the actual environment of an assembly. On the other hand, 3D direct transport calculations and the 2D/1D Fusion method, mostly based on the method of characteristics, have recently been applied showing excellent agreement with reference Monte-Carlo code, but still remaining computationally expensive for multiphysics applications and core depletioncalculations.In the present work, we propose a method of Dynamic Homogenization as an alternative technique for 3D core calculations, in the framework of domain decomposition method that can be massively parallelized. It consists of an iterative process between core and assembly calculationsthat preserves assembly exchanges. The main features of this approach are:i) cross-sections homogenization takes into account the environment of each assembly in the core;ii) the reflector can be homogenized with its realistic 2D geometry and its environment;iii) the method avoids expensive 3D transport calculations;iv) no “off-line” calculation and therefore v) no cross-section interpolation is required.The verification tests on 2D and 3D full core problems are presented applying several homogenization and equivalence techniques, comparing against direct 3D transport calculation. For this analysis, we solved the NEA “PWR MOX/UO2 Core Benchmark” problem, which is characterized by strong radial heterogeneities due to the presence of different types of UOx and MOx assemblies at different burnups. The obtained results show the advantages of the proposed method in terms of precision with respect to two-step and performances with respect to the direct approach
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Chudyk, Ewa Iwona. "Calculating free energy profiles for enzyme catalysed reactions." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633252.
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Hydrolysis of biologically active compounds by enzymes is one of the most important processes in living organisms. This thesis describes the use of molecular dynamics (MD) simulations and free energy calculations to investigate two types of enzymes that catalyse hydrolysis reactions: fatty acid amide hydrolase, a target for antidepressant drugs, and class A B-lactamases, responsible for emerging antibiotic resistance in bacteria. Fatty acid amide hydrolase (FAAH) is an enzyme that deactivates neurotransmitters involved in inducing sleep, anxiety, inflammatory and pain states. To investigate catalysis in FAAH, an empirical valence bond approach was used to study the first step of acylation with oleamide. Results from this approach were compared with previous quantum mechanics/molecular mechanics (QM/MM) potential energy simulations and with experimental data. Further analysis of the FAAH active site indicated residues important for catalysis, which may provide insight for inhibitor design.
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Wei, Chunyang. "Thermal runaway reaction hazard and decomposition mechanism of the hydroxylamine system." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4154.
Full textAbstract:
Chemical reactivity hazards have posed a significant challenge for industries that
manufacture, store, and handle reactive chemicals. Without proper management and
control of reactivity, numerous incidents have caused tremendous loss of property and
human lives. The U.S. Chemical Safety and Hazard Investigation Board (CSB) reported
167 incidents involving reactive chemicals that occurred in the U.S. from 1980 to 2001.
According to the report, 35 percent of the incidents were caused by thermal runaway
reactions, such as incidents that involved hydroxylamine and hydroxylamine nitrate.
The thermal stability of hydroxylamine system under various industrial
conditions was studied thoroughly to develop an understanding necessary to prevent
recurrence of incidents. The macroscopic runaway reaction behavior of hydroxylamine
system was analyzed using a RSST (Reactive System Screening Tool) and an APTAC
(Automatic Pressure Tracking Calorimeter). Also, computational chemistry was
employed as a powerful tool to evaluate and predict the measured reactivity. A method
was proposed to develop a runaway reaction mechanism that provides atomic level ofinformation on elementary reaction steps, in terms of reaction thermochemistry,
activation barriers, and reaction rates.
This work aims to bridge molecular and macroscopic scales for process safety
regarding reactive chemicals and to understand macroscopic runaway reaction behaviors
from a molecular point of view.