Mechanism and kinetics for the reaction of DMSO with O(P-3) have been investigated by M06-2X/MG3S, CBS-QB3 and G4MP2 methods. Four possible reaction pathways are identified. Among them, the O(P-3) addition to S-atom followed by CH3 elimination is almost exclusive. Four pre-reactive complexes have been located. AIM theory is used to determine the nature of interactions in these complexes. Considering the formation of pre-reactive complex, the rate constant for major pathway is calculated using transition state theory applied to a two-step mechanism. Enthalpies of formation at 298.15 K (Delta H-f degrees(298.15)) have been calculated using the composite CBS-QB3, G4MP2 and G3B3 methods. (C) 2012 Elsevier B.V. All rights reserved.