Kinetics and Mechanism of the O Atom Reaction with Dimethyl Sulfoxide

Abstract

The kinetics and mechanism of the reaction O + DMSO → products (1) have been studied by the mass spectrometric discharge-flow method at 298 K and at a total pressure of 1 Torr of helium. The reaction rate coefficient was measured under pseudo-first-order conditions either from the kinetics of O atom consumption in excess of DMSO or from the kinetics of DMSO decay in excess of O atoms: k1 = (1.0 ± 0.2) × 10-11 cm3molecule-1s-1 (uncertainty includes 2σ statistical error and estimated systematic errors). Both CH3 and SO2 were detected as the products of reaction 1, and the reaction O + DMSO → 2CH3 +SO2 was found to be the main (if not unique) channel of reaction 1 under the experimental conditions of the study. This result indicates that reaction 1 cannot be a suitable laboratory source of the atmospheric relevant CH3SO2 radical, at least at low pressures. In addition, the upper limits, k3 < 1 × 10-13 and k4 < 5 × 10-15 cm3 molecule-1 s-1, were determined for the rate coefficients of the reactions CH3 + DMSO → products (3) and Br2 + DMSO → products (4), respectively. The rate constant of the self-combination of CH3 radicals, CH3 + CH3 (+M) → C2H6 (+M) (2), was also determined in the pressure range between 0.5 and 3.0 Torr of He.