Reaction of Atmospherically Relevant Sulfur-Centered Radicals with RO 2 and HO 2 .

The atmospheric oxidation of dimethyl sulfide and other emitted sulfur species leads to the formation of the methylthio radical, CH 3 S, which can be further oxidized to the CH 3 SO and CH 3 SO 2 radicals. We investigated computationally the reactions of these three sulfur-centered radicals with the peroxy radicals ROO and HOO. Our results demonstrate that CH 3 S and CH 3 SO react with these peroxy radicals to form short-lived peroxide intermediates, which then decompose via a concerted O-O bond scission and S═O double bond formation that results in an increased valence of the sulfur atom. In contrast, CH 3 SO 2 reacts to form stable CH 3 S(O) 2 OOR and CH 3 S(O) 2 OOH peroxide products, as sulfur is already at its highest valence. Multireference methods were used to describe these reactions in which the valence of the sulfur atom changes.