Date of Award

Spring 2023

Document Type

Thesis

Terms of Use

© 2023 Rory R. Schmidt. This work is freely available courtesy of the author. It may be used under the terms of the Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license. For all other uses, please contact the copyright holder.

Creative Commons License

Creative Commons Attribution-Share Alike 4.0 International License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.

Degree Name

Bachelor of Arts

Department

Chemistry & Biochemistry

First Advisor

Thomas Alex Stephenson

Abstract

Isoprene ozonolysis is a major atmospheric producer of atmospheric oxidizers and aerosols. This complex reaction pathway forms an exothermic cascade, where constant competition between bimolecular sinks, unimolecular isomerizations, and collisional relaxation dictate reactivity. This work focuses on two isoprene derived Criegee intermediates, methacrolein oxide (MACR oxide) and formaldehyde oxide (FO). While the potential energy surface of FO is well understood, the reactivity of energetically excited FO has not been explored in detail. MACR oxide isomerization and primary products have been adequately characterized and explored computationally and experimentally, but the potential energy surface beyond isopropenyl dioxirane has not received the same treatment. Using combinations of DFT and CAS model chemistries, a potential energy surface starting at FO was constructed, leading to formic acid and other dissociation sink species. The novel MACR oxide potential energy surface was modeled after the FO potential energy surface, from isoprene derived isopropenyl dioxirane, through a diradical intermediate, to ester, acid and dissociation sink species. An abundance of conformational isomerism, as well as the potential for a valley ridge inflection point, were investigated as features of this potential energy surface. Both potential energy surfaces were analyzed using MESMER, the Master Equation Solver for Multi Energy Well Reactions, at temperatures and pressures indicative of an isoprene rich atmosphere, at varying levels of thermal and chemical excitation. The FO system was found to be dominated by thermal reactivity at all but the highest levels of chemical excitation. The MACR oxide system featured three phases of reactivity, two prompt and one thermalized, featuring temperature and phase dependent product branching ratios for our sink species. Our results serve to illuminate an otherwise unexplored corner of the reactivity of common Criegee intermediates.

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