Formation of OH radicals from the simplest Criegee intermediate CH2OO and water

Abstract

Hydroxyl (OH) radicals can convert nitrogen and sulfur oxides to nitric and sulfuric acid, respectively, and oxidize nonmethane hydrocarbons to organic acids, which play an important key role in the environmental chemistry. The famous Criegee intermediates (CIs) are also key species in atmospheric chemistry. The most important loss paths that control CIs levels are suggested to be the reaction with water vapor. To study the reaction mechanism of the simplest CI (CH2OO) with H2O, stationary species and saddle points on the potential energy surface (PES) of CH2OO + H2O have been investigated at CCSD(T)/AUG-cc-pVTZ//B3LYP/6-311++G(2d,2p) level of theory. The computational results indicate that the most feasible channel for the reaction of CH2OO with H2O produces HOCH2O and hydroxyl radicals (OH). Because the highest Gibbs free energy barrier is only 10.5 kcal/mol, this path will be active in atmosphere and OH radical can be produced in this process. Besides, we find a transition state which has not been reported before and explained the mechanism of the formation of a key intermediate. We also scan the formation PES of OH radical from an intermediate and find a loose transition state, which illustrates the mechanism of the producing of OH radical in the reaction of CH2OO with H2O. Here we present a new way of producing OH radicals.