Mechanistic and Kinetic Study of the Gas-Phase Reaction of Hydroxyl Radical with Dimethyl Sulfoxide

Time-resolved tunable diode laser spectroscopic detection of CH 3, CH 4, and SO 2 has been coupled with 248 nm laser flash photolysis of H 2 O 2 in the presence of CH 3 S(O)CH 3 (DMSO) to study the mechanism and kinetics of the OH + DMSO reaction at 298 K. Production of CH 3 from the OH + DMSO reaction in the presence of N 2 buffer gas is observed. The rate-limiting step in CH 3 production is found to be the OH + DMSO reaction under all experimental conditions investigated (including first-order CH 3 production rates up to 10 5 s -1 ), suggesting that a stabilized OH−DMSO adduct, if formed, has a lifetime of less than 10 μs toward methyl elimination at 298 K and 20 Torr total pressure. From measurements of the CH 3 appearance rate as a function of DMSO concentration, a rate coefficient of k 1 = (8.7 ± 1.6) × 10 -11 cm 3 molecule -1 s -1 is obtained for the OH + DMSO reaction. Using the OH + CH 4 reaction as a “unit yield calibration”, the CH 3 yield from OH + DMSO is found to be 0.98 ± 0.12. The uncertainties in k 1 and the CH 3 yield are 2σ and include estimates of systematic errors. Neither CH 4 nor SO 2 are observed as products of the OH + DMSO reaction. Upper limits (95% confidence limits) on the yields of CH 4 and SO 2 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.