ATMOSPHERIC CHEMISTRY OF CH2BR2 - RATE COEFFICIENTS FOR ITS REACTION WITH CL ATOMS AND OH AND THE CHEMISTRY OF THE CHBR2O RADICAL

Rate coefficients for the reaction of OH radicals and Cl atoms with di bromomethane, OH + CH2Br2 --> CHBr2 + H2O (1) and Cl + CH2Br2 --> CHBr 2 + HCl (3), and for the reaction of Cl atoms with methyl bromide, Cl + CH3Br --> HCl + CH2Br (4), have been obtained using relative rate te chniques. At 298 K, the value of k(1) was determined to be (1.2 +/- 0. 3) x 10(-13) cm(3) molec(-1) s(-1). The rate coefficients k(3) and k(4 ) were determined at a series of temperatures ranging from 228 K to 29 6 K and combined with the measurements of Gierczak et al., yielding th e following Arrhenius expressions for k(3) and k(4); k(3) = (6.35 +/- 0.6) x 10(-12) exp(-807 +/- 50/T) cm(3) molec(-1) s(-1) and k(4) = (1. 49 +/- 0.2) x 10(-11) exp(-1056 +/- 50/T) cm(3) molec(-1) s(-1). In ad dition, 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 a mounts of CO. The dominant atmospheric fate of the alkoxy radical, CHB r2O, is elimination of a Br atom, which occurs at the rate estimated t o be greater than 4 x 10(6) s(-1) in 700 torr of O-2 at 298 K. (C) 199 6 John Wiley & Sons, Inc.