Theoretical kinetics studies on the temperature and pressure dependence of the reaction of ammonia with the Criegee intermediate CH2OO

In present theoretical research work, the mechanism and kinetics for the reaction of the Criegee intermediate, CH2OO, with NH3 molecule is investigated in detail. After optimizing the structures of the reactants, intermediates, saddle-point structures and products of the reaction at the M11L/Aug-cc-pVTZ level, accurate energies are obtained by W1RO and post-CCSD(T) electronic structure methods. In addition to the initial adduct methyl amine hydroperoxide (MAHP), four reaction pathways are determined as possible product channels for CH2OO + NH3 reaction including CH2(O)NH2· + OH· (P1), H2NC(O)H + H2O (P2), H2CNH + HOOH (P3) and H2CNH + H2OO (P4). The rate coefficients for the formation of products are calculated by statistical rate theories. The effect of the pre-reactive complex mentioned in previous theoretical and experimental studies on the reaction rate is accounted for by a two transition-state model. The adduct methyl amine hydroperoxide (MAHP) and CH2(O)NH2· + OH· (P1) are found to be the significant products of the title reaction. At lower altitudes of troposphere, MAHP is predicted to be the dominant product with a branching ratio about 98.5%. However, at higher altitudes where temperature increases and pressure drops, the product channel CH2(O)NH2· + OH· become significant.