Improved rate coefficient expressions for the reaction of methyl bromide with OH and Cl radicals

Abstract

Methyl bromide (CH3Br) is a hazardous ozone depleting substance that is released to the atmosphere from natural and anthropogenic sources. Within the troposphere CH3Br is removed through reaction with [rad]OH and Cl[rad] radicals. Here, quantum and statistical mechanical calculations are combined with existing experimental data in order to arrive at improved rate coefficient expressions for the reaction of methyl bromide with [rad]OH and Cl[rad] from 200 to 2000 K. For CH3Br + [rad]OH k = 9.8 × 10−14 (T/298)2.9 exp(−3000/RT) and for CH3Br + Cl[rad] k = 1.5 × 10−12 (T/298)2.0 exp(−2900/RT), with k in cm3 molecule−1 s−1, T in K, and R = 1.987 cal mol−1 K−1.