Bimolecular reactions involving stabilized Criegee Intermediates (SCI) have been the target of many studies due to the role these molecules play in atmospheric chemistry. Recently, kinetic rates for the addition reaction of the simplest SCI (formaldehyde oxide) and its methylated analogue (acetone oxide) with methanol were reported both experimentally and theoretically. We re-examine the energy profile of these reactions by employing rigorous <i>ab initio</i> methods and explore the temperature dependence of the kinetic properties. Optimized CCSD(T)/ANO1 geometries are reported for the stationary points along the reaction path. Energies are obtained at the CCSD(T)/CBS level of theory with corrections that include contributions of full triple and quadruple excitations. We show that the inclusion of high-order excitations in the coupled cluster method can raise the barrier of these reaction up to 0.83 kcal mol<sup>-1</sup>, which has a significant impact on kinetic predictions. Conventional Canonical Transition State Theory (CTST) rates are reported for a range of temperatures. Partition functions are computed under the Rigid Rotor Harmonic Oscillator approximation (RRHO) and with the inclusion of a one-dimensional rigid rotor treatment. The corrections for internal rotations have a significant impact on computed kinetic rates and thermodynamic functions. We conclude that the different temperature dependencies observed experimentally for the two SCI are mainly due the height of the transition state barrier. Additionally, we find the negative temperature dependence of the reaction rate observed for acetone oxide at low temperatures is sensitive to the tunneling contribution.

Theoretical investigation of the addition of methanol to criegee intermediates

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.