Formation pathways of DMSO 2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO 2 ) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO x ) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO 2 from the CH 3 S(O)(OH)CH 3 adduct [including the formation of CH 3 S(O)(OH)CH 3 from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO 2 from the CH 3 S(O 2 )(OH)CH 3 adduct are also studied. The formation of the CH 3 S(O 2 )(OH)CH 3 adduct from CH 3 S(OH)CH 3 (DMS‐OH) and O 2 was analyzed in our previous work. All these pathways due to the presence of NO x (NO and NO 2 ) and also due to the reactions with O 2 , OH and HO 2 are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO 2 (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO x ‐dependent pathways leading to the formation of DMSO 2 , which could explain some of these experimental results in comparison with experimental measurements carried out in NO x ‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009