Quantum Chemical Studies of the Thermal and Photo-induced Chemistry of Criegee Intermediates.

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This project is being jointly funded by the Environmental Chemical Sciences (ECS) and the Chemical Theory, Modeling, and Computation (CTMC) Programs of the Chemistry Division, as well as the Established Program to Stimulate Competitive Research (EPSCoR). Professor Tolga Karsili of the University of Louisiana at Lafayette and his students are using and developing state-of-the-art quantum chemical and dynamics methods to study the chemistry of Criegee intermediates (CI). CIs are formed by the reaction of ozone with volatile organic compounds in the atmosphere. Such reactions are an important source of hydroxyl radicals which break down pollutants and ‘clean’ the atmosphere. They are often referred to as atmospheric detergents and are important in increasing the oxidizing capacity of the atmosphere. The project involves graduate and undergraduate students, as well as high-school students, including members of underrepresented groups. The students also have opportunities to travel to the group of the collaborator, Professor Hua Guo (University of New Mexico), to learn new techniques. The project focusses on the unimolecular decay of the thermalized and vibrationally and electronically excited CIs. CIs are formed with excess internal energy and thus may undergo further reactions, such as unimolecular decay or isomerization. Alternatively, the highly vibrationally excited CI may undergo vibrational energy relaxation through collisions with proximal molecules. The stabilized CIs can then undergo unimolecular decay, react with several trace atmospheric species or may undergo UV-excitation. Unimolecular decay of thermalized and highly vibrationally excited CI is a well-known source of hydroxyl radicals. Professor Karsili and his group are computationally studying the vibrationally and electronically excited quantum dynamics associated with the simplest CI, derived from the ozonolysis of ethene and then systematically comparing with CIs of increasing molecular complexity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.