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Title: Semiclassical transition state theory for chemical reactions : theory, development and applications
Author: Burd, Timothy Alan Harvey
ISNI:       0000 0004 9356 8331
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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Semiclassical Transition State Theory (SCTST) is an efficient rate theory, which aims to calculate the rate constants of chemical reactions, including quantum tunnelling effects, without requiring a global potential energy surface. It has applications in understanding chemical reactions involving medium sized molecules where more computationally expensive methods are not possible. The work in this thesis aims to increase our understanding of the theory, apply the method to interesting problems in chemistry, and develop the method for the study of a broader range of systems and problems. The Theory section of this thesis begins with a review of the theoretical basis of SCTST. We then illustrate how the theory can be adapted for treating complex systems with internal rotational degrees of freedom, and higher orders of perturbation theory. We then show that the SCTST method implicitly accounts for key multidimensional effects, such as corner-cutting and variational effects, and identify the limitations of this approach. In the Applications section, we apply SCTST to the study of a range of chemical problems. We show that SCTST in full and reduced dimensions can be used to help understand the decay of Criegee intermediates in the atmosphere, and identify a water-catalysed route that contributes significantly to the decay process. By studying enol-formation from a phenyl pyruvic acid derivative, we provide evidence for an alternative reaction mechanism, consistent with recently performed experiments. In the Development section, efforts to adapt the method to increase its range of applicability are then described. A reduced dimensional form of SCTST is discussed and shown to be particularly efficient, where the required number of electronic structure calculations is reduced to an absolute minimum. We also show how the SCTST rate equations can be recast to calculate tunnelling splittings in chemical systems in a reliable and cost efficient way. Finally, we present a user friendly code base for SCTST calculations, made freely available for download, called pySCTST.
Supervisor: Clary, David Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available