Mechanistic and kinetic study of the gas-phase reaction of hydroxyl radical with dimethyl sulfoxide

Time-resolved tunable diode laser spectroscopic detection of CH3, CH4, and SO2 has been coupled with 248 nm laser flash photolysis of H2O2 in the presence of CH3S(O)CH3 (DMSO) to study the mechanism and kinetics of the OH + DMSO reaction at 298 K. Production of CH3 from the OH + DMSO reaction in the presence of N-2 buffer gas is observed. The rate-limiting step in CH3 production is found to be the OH + DMSO reaction under all experimental conditions investigated (including first-order CH3 production rates up to 10(5) s(-1)), suggesting that a stabilized OH-DMSO adduct, if formed, has a lifetime of less than 10 mu s toward methyl elimination at 298 K and 20 Torr total pressure. From measurements of the CH3 appearance rate as a function of DMSO concentration, a rate coefficient of k(1) = (8.7 +/- 1.6) x 10-(11) cm(3) molecule(-1) s(-1) is obtained for the OH + DMSO reaction. Using the OH + CH4 reaction as a "unit yield calibration", the CH3 yield from OH + DMSO is found to be 0.98 +/- 0.12. The uncertainties in k(1) and the CH3 yield are 2 sigma and include estimates of systematic errors. Neither CH4 nor SO2 are observed as products of the OH + DMSO reaction. Upper limits (95% confidence limits) on, the yields of CH4 and SO2 both in the presence and absence of O-2 are found to be 0.04 and 0.06, respectively. The atmospheric implications of our findings in the context of previous laboratory studies and atmospheric field measurements are discussed.