Variational transition-state theory study of the dimethyl sulfoxide (DMSO) and OH reaction.

The mechanism for the atmospheric oxidation of DMSO has been studied. For the first time, all the possible channels in the DMSO + OH reaction are studied together theoretically, and their corresponding rate constants have been evaluated under the variational transition-state formalism. Three different channels have been characterized: an addition-elimination process to form MSIA (CH3SOOH) and CH3, a H-abstraction pathway to give CH3SOCH2 and H2O, and a nonkinetically relevant S(N)2-type reaction to form methanol and CH3SO. In agreement with previous experimental and theoretical works, the main product in the DMSO + OH reaction turns out to be the MSIA, with a branching ratio at 298.15 K around 97%. The effects of pressure in the global rate constant have also been analyzed.