Models for Atmospheric Organic Nitrate-Forming Reactions

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The goal of this work is to determine the fundamental dynamics of key organic nitrate-forming reactions and develop predictive models of this chemistry. It is hypothesized that the master equation (ME) approach for this class of reactions suffers from a failure of Rice-Ramsperger-Kassel-Marcus (RRKM) theory because of slow intramolecular vibrational energy redistribution (IVR). Quasi-classical trajectory (QCT) calculations will be used to assess the importance of slow IVR in the reaction system consisting of peroxy radicals (RO2) with nitric oxide (NO) to form alkoxy radicals (RO) or alkyl nitrates (RONO2). When feasible, analytical potential energy surfaces will be constructed; direct dynamics with a parameterized semiempirical quantum theory like NDDO-SRP (neglect of diatomic differential overlap - specific reaction parameters) will also be used to calculate the potential and its gradients. Both approaches will be evaluated using high level electronic structure calculations. Temperature and pressure-dependent yields of nitrates from nitrate radical (NO3) + alkene reactions of primary and secondary alkenes as a function of carbon chain length will also be calculated. The results will enable other researchers to develop accurate atmospheric chemistry models to predict atmospheric nitrate yields as a function of temperature, pressure, and the identity of the RO2 radical or alkene. All parameterizations, ME source codes, and models will be made freely available on the internet. Insights into non-RRKM kinetics will be applicable to the study of other non-equilibrium systems, such as in combustion. Students and postdoctoral research associates will learn about chemical kinetics theory, QCT dynamics, and quantum chemistry methods in the context of atmospheric chemistry.