Methoxysulfinyl Radical CHOSO: Gas-Phase Generation, Photochemistry, and Oxidation.

Methylsulfoxide radicals CHSO (x = 1-4) are key reactive sulfur species (RSS) in the atmospheric oxidation of volatile organic sulfur compounds (VOSCs). Through flash vacuum pyrolysis (FVP) of trifluoromethanesulfinic acid methyl ester CFS(O)OCH at 1000 K, the methoxysulfinyl radical CHOSO has been generated in the gas phase and subsequently characterized in cryogenic N, Ar, and Ne matrices by IR spectroscopy. Upon 266 nm laser irradiation, CHOSO efficiently isomerizes to the less stable methylsulfonyl radical CHSO in matrices without noticeable decomposition. In the gas phase, CHOSO reacts with O and yields sulfinyl peroxyl radical CHOS(O)OO, a new member in the CHSO (x = 1-4) family. This radical dissociates into SO and CHO with the intermediacy of the sulfonyoxyl radical CHOSO under the 266 nm laser irradiation. Additionally, the photoisomerization of CFS(O)OCH to sulfenic ester CFOSOCH was also observed.