An FTIR product study of the photooxidation of dimethyl disulfide

The products of the 254 nm photolysis of ppm levels of DMDS have been studied as a function of the O₂ partial pressure at 760 Torr (N₂ + O₂) and 298±2 K. The major sulfur containing compounds detected were SO₂ and CH₃SO₃H (methane sulfonic acid, MSA) and the major carbon containing compounds were CO, HCHO, CH₃OH and CH₃OOH (methyl hydroperoxide). Within the experimental error limits the observed sulfur and carbon balances were approximately 100%. CH₃OOH has been observed for the first time in such a photooxidation system. Its observation provides evidence for the formation of CH₃ radicals by the further oxidation of the CH₃S radicals formed in the primary photolysis step.From the behavior of the DMDS photolysis products as a function of the O₂ partial pressure, O₃ concentration and added OH radical source it is postulated that the further reactions of CH₃SOH (methyl sulfenic acid), formed in the reaction OH + CH₃SCCH₃ CH₃SOH + CH₃S, are the main source of MSA in the 254 nm photolysis of DMDS.Some of the possible implications of the results of this study for the degradation mechanisms of other atmospherically important organic sulfur compounds, in particular DMS, are briefly considered.