Theoretical study on the reaction mechanism of CH2ClO2 with HO2

The complex potential energy surface for the reaction of CH2ClO2 with HO2, including 12 intermediates, 31 interconversion transition states and 16 major dissociation products, was theoretically probed at the G2MP2//B3LYP/6-311G(2d,2p) level of theory. The geometries and relative energies for various stationary points were determined. Based on the calculated G2MP2 potential energy surface, the possible mechanism for the reaction of CH2ClO2 with HO2 was proposed. It is shown that the most feasible channels are those leading to CH2ClOOH + 3O2, CHClO2 + H2O2, CH2ClOH + O3 and CH2O + 2Cl + 2HOOO, with the energy barriers of 17.0, 22.6, 24.5 and 24.5 kcal/mol, respectively. Among them, the formations of the first product is a one-step reaction, while the others are produced via CH2ClO2 and HO2 by forming a tetroxide intermediate first, then the intermediate dissociates to yield productions or through multi-steps reactions via several transition states and intermediates to produce the final products. Our results suggest that besides CH2ClOOH + 3O2, it is also possible for the reaction of CH2ClO2 with HO2 to form the others. In addition, most of the product CH2ClOOH will undergo secondary dissociation to yield HC(O)Cl and H2O via a barrier of 45.9 kcal/mol. And the secondary decomposition of the product HOOO gives 2OH and O2 with a small barrier of 3.8 kcal/mol.