Reactions of the methylsulfinyl radical [CH 3 (O)S˙] with oxygen ( 3 O 2 ) in solid argon

The atmospherically highly relevant methylsulfinyl radical (CH 3 (O)S˙) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of 3 O 2 . Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed 3 O 2 adduct has the structure of a peroxyl radical (CH 3 (O)SOO˙), which upon irradiation with UV light isomerizes to the methylsulfonoxyl radical (CH 3 SO 3 ˙). The latter transforms into the methansulfonic acid radical (˙CH 2 SO 3 H) by irradiation with visible light. During the matrix photolysis small amounts of SO 3 and the methyl radical were detected indicating competitive direct photodissociation.