Reactions of the methylsulfinyl radical [CH3(O)S˙] with oxygen ((3)O2) in solid argon.

The atmospherically highly relevant methylsulfinyl radical (CH3(O)S˙) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of (3)O2. Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed (3)O2 adduct has the structure of a peroxyl radical (CH3(O)SOO˙), which upon irradiation with UV light isomerizes to the methylsulfonoxyl radical (CH3SO3˙). The latter transforms into the methansulfonic acid radical (˙CH2SO3H) by irradiation with visible light. During the matrix photolysis small amounts of SO3 and the methyl radical were detected indicating competitive direct photodissociation.