Quantitative kinetics for the atmospheric reactions of Criegee intermediates with acetonitrile

Abstract

Obtaining quantitative kinetics of Criegee intermediates is of paramount significance in the atmosphere. However, there are limited reports on the kinetics of Criegee intermediates. Here, by using our very recently developed dual-level strategy, we report the quantitative kinetics of the reaction of Criegee intermediates (CH₂OO/anti-CH₃CHOO/syn-CH₃CHOO) with acetonitrile (CH₃CN). The dual-level strategy combines post-CCSD(T) calculations for transition state theory with the validated M06CR/MG3S and M11-L/MG3S functional methods for direct dynamics calculations using canonical variational transition state theory with small-curvature tunneling to obtain recrossing effects and tunneling coefficients. We show that W3X-L//DF-CCSD(T)-F12b/jun-cc-pVDZ can be used to obtain quantitative enthalpies of activation at 0 K in the reactions of Criegee intermediates with CH₃CN. We find that the CH₂OO/anti-CH₃CHOO/syn-CH₃CHOO + CH₃CN reactions only depend on temperature. Moreover, we also find that their rate constants are dominantly determined by the enthalpy of activation at 0 K and recrossing effects and tunneling are negligible. The present findings also show that the CH₂OO/anti-CH₃CHOO + CH₃CN reactions have negative temperature dependence in the range of 190–350 K. In the atmosphere, we reveal that the reactions of CH₂OO and anti-CH₃CHOO with CH₃CN are significant acetonitrile sinks, leading to the formation of N-formylacetamide and diacetamide. The present findings will be useful for obtaining quantitative kinetics of Criegee intermediates and understanding acetonitrile sinks.