A quantum chemical study on •Cl-initiated atmospheric degradation of CH2BrO2•

Abstract

The singlet and triplet potential energy surfaces for the CH2BrO2• + •Cl reaction have been researched theoretically. All of the probable reaction routes were investigated by using B3LYP and G3(MP2) models. Addition/elimination and SN2 displacement exist on the singlet potential energy surfaces (PES), and the foremost approach process of CH2BrO2• + •Cl is generating IM1 (CH2BrOOCl) with no barrier, followed by the O-O bond breaking accompanied by an H-migrate resulting in the most abundant product P1 (CHBrO + HClO). One direct H-abstraction and three SN2 displacement reaction pathways exist on the triplet PES, and direct H-abstraction is the foremost pathway. RRKM-TST theory was employed to predict product distribution of the CH2BrO2• + •Cl reaction. At atmospheric pressure, the production of P1 (CHBrO + HClO) by addition/elimination dominants the reaction at T ≤ 800 K, while the direct H-abstraction takes over the reaction at T > 800 K. The total rate constants are insensitive to pressure, and the branching rate constants are just the opposite. The lifetime of CH2BrO2• in the presence of •Cl was predicted to 3.2 d. Moreover, time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CH2BrOOCl), IM2 (CH2BrOClO) and IM3 (CH2(OBr)OCl) will photolyze under the sunlight.