Temperature-dependent kinetics of the simplest Criegee intermediate reaction with dimethyl sulfoxide

Criegee intermediates are thought to play roles in atmospheric chemistry, including OH radical formation, oxidation of SO2, NO2, etc. CH2OO is the simplest Criegee intermediate, of which the reactivity has been a hot topic. Here we investigated the kinetics of CH2OO reaction with dimethyl sulfoxide (DMSO) under 278-349 K and 10-150 Torr. DMSO is an important species formed in the oxidation of dimethyl sulfide in the biogenic sulfur cycle. The concentration of CH2OO was monitored in real-time via its mid-infrared absorption band at about 1,286 cm(-1)(Q branch of the nu(4)band) with a high-resolution quantum cascade laser spectrometer. The 298 K bimolecular rate coefficient was determined to bek(298)= (2.3 +/- 0.3) x 10(-12)cm(3)/s at 30 Torr with an Arrhenius activation energy of -3.9 +/- 0.2 kcal/mol and a weak pressure dependence for pressures higher than 30 Torr (k(298)= (2.8 +/- 0.3) x 10(-12)cm(3)/s at 100 Torr). The reaction is speculated to undergo a five-membered ring intermediate, analogous to that of CH2OO with SO2. The negative activation energy indicates that the rate-determining transition state is submerged. The magnitude of the reaction rate coefficient lies in between those of CH2OO reactions with (CH3)(2)CO and with SO2.