Atmospheric chemistry of CH2BR2: Rate coefficients for its reaction with Cl atoms and OH and the chemistry of the CHBr2O radical

Abstract

Rate coefficients for the reaction of OH radicals and Cl atoms with dibromomethane OH + CH2Br2 → CHBr2 + H2O (1) and Cl + CH2 Br2 → CHBr2 + HCL (3) and for the reaction of Cl atoms with methyl bromide, Cl + CH3Br → HCl + CH2Br (4), have been obtained using relative rate techniques. At 298 K, the value of k1 was determined to be (1.2 ± 0.31) × 10−13 cm3 molec−1 s−1. The rate coefficients k3 and k4 were determined at a series of temperatures ranging from 228 K to 296 K and combined with the measurements of Gierczak et al., yielding the following Arrhenius expressions for k3 and k4; k3 = (6.35 ± 0.6) × 10−12 exp(−807 ± 50/T) cm3 molec−1 s−1 and k4 = (1.49 ± 0.2) × 10−11 exp(−1056 ± 50/T) cm3 molec−1 s−1. In addition, the Cl atom initiated oxidation mechanism of CH2Br2 in air has been studied at 298 K. The products observed were HC(O)Br and small amounts of CO. The dominant atmospheric fate of the alkoxy radical, CHBr2O is elimination of a Br atom, which occurs at a rate estimated to be greater than 4 × 106 s−1 in 700 torr of O2 at 298 K. © 1996 John Wiley & Sons, Inc.