Theoretical study on HO _2-initiated atmospheric oxidation of halogenated carbonyls

摘要

The initial reactions of HO _2 with oxalyl dichloride, oxalyl dibromide, acetyl chloride, and acetyl bromide are studied for the first time using the density functional theory with CAM-B3LYP and wB97XD, CBS-QB3, and G3 theoretical methods and the transition state theory. The reactions occur via the similar mechanism that the prereactive complex is formed before the transition state and product. The calculated results demonstrate that the HO _2 radical with ClC(O)C(O)Cl and BrC(O)C(O)Br reactions is feasible and could play a significant role in the atmosphere because the barriers are 0.13 kcal/mol, -0.05 kcal/mol with respect to the free reactants, respectively at the CBS-QB3 level of theory. In addition, the rate constants of the HO 2 + ClC(O)C(O)Cl and HO _2 + BrC(O)C(O)Br reactions are computed to be 1.37 ×10 ~(-15)cm ~3 mol ~(-1) s ~(-1), 1.70 ×10 ~(-15) cm ~3 mol ~(-1) s ~(-1) at 298 K. However, the HO _2 reactions with acetyl chloride and acetyl bromide are of no importance because of higher activated barrier and slower rate constant.