FT-IR kinetic and product study of the Br-initiated oxidation of dimethyl sulfide

An FT-IR kinetic and product study of the Br-atom-initiated oxidation of di methyl sulfide (DMS) has been performed in a large-volume reaction chamber at 298 K and 1000 mbar total pressure as a function of the bath gas composi tion (N-2 + O-2). In the kinetic investigations using the relative kinetic method, considerable scatter was observed between individual determinations of the rate coefficient, suggesting the possibility of interference from s econdary chemistry in the reaction system involving dimethyl sulfoxide (DMS O) formation. Despite the experimental difficulties, an overall bimolecular rate coefficient for the reaction of Br atoms with DMS under atmospheric c onditions at 298 K of less than or equal to 1 x 10(-13) cm(3) molecule(-1) s(-1) can be deduced. The major sulfur products observed included SO2, CH3S Br, and DMSO. The kinetic observations in combination with the product stud ies under the conditions employed are consistent with rapid addition of Br atoms to DMS forming an adduct that mainly re-forms reactants but can also decompose unimolecularly to form CH3SBr and CH3 radicals. The observed form ation of DMSO is attributed to reactions of BrO radicals with DMS rather th an reaction of the Br-DMS adduct with O-2 as has been previously speculated and is thought to be responsible for the variability of the measured rate coefficient, The reaction CH3O2 + Br --> BrO + CH3O is postulated as the so urce of BrO radicals. (C) 1994 John Wiley & Sons, Inc.