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An analysis of the sources and sinks for Criegee intermediates: An extended computational study

Watson, Nathan 2021. An analysis of the sources and sinks for Criegee intermediates: An extended computational study. PhD Thesis, Cardiff University.
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Abstract

This thesis is centred around a common theme of using computational chemistry to investigate reactions that either produce or deplete atmospheric Criegee intermediates (CIs). The computational work investigates many novel reaction mechanisms and generates kinetic and product branching data for these reactions which is then reviewed in the context of their impact on local tropospheric environments. Firstly, the ozonolysis of a large array of alkenes is examined, as known sources of CIs. The results of this study indicate that factors including the number of α-H atoms in the alkene substituents and others besides all have a significant influence on the ozonolysis rate constants and the fractional distribution of different CI yields. Assessments of bimolecular CI sinks are also examined, particularly via reaction with gaseous alcohols. The high reactivity of many CI + alcohol reactions shows that in geographical areas such as Sao Paulo, where biofuel use is prevalent, that alcohols are likely a significant sink of CIs. The bimolecular chemistry of a series of CIs derived from a new range of synthetic hydrofluoroolefin refrigerants are also examined, because their refrigerant precursors are being emitted in ever larger quantities, and their fluorinated substituents make their CI chemistry distinctive. Both the CIs and their alkene precursors are classified into several sets of taxonomic groups on the basis of common structural features and similar bimolecular chemistries. By linking computational ozonolysis chemistry to the structural alkene features, this classification allows the author to generate a new theoretical “FESP” model designed to predict the ozonolysis chemistry of lengthy, conformationally flexible alkenes. This model is used to determine the reaction rate and branching fractions of the O3 + Z-2-hexene reaction, but could be applied to many other alkenes, and perhaps even adapted to explore the bimolecular reactivity of lengthy CIs.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 7 October 2021
Last Modified: 08 Oct 2021 10:16
URI: https://orca.cardiff.ac.uk/id/eprint/144742

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