KINETICS OF THE RECOMBINATION REACTION SH-2+AR - IMPLICATIONS FOR THEFORMATION AND LOSS OF HSOO AND SOO IN THE ATMOSPHERE(O)

Unimolecular pathways for the dissociation of thiylperoxyl have been i nvestigated computationally. Gaussian-2 (G2) theory was employed to ca lculate the thermochemistry, and the kinetics of SH + O-2 --> HSOO are analyzed by RRKM theory. Under atmospheric conditions the rate consta nt is close to the low-pressure limit of k(0) approximate to 9.2 x 10( -34)(T/298 K)(-1.69) molecule(-2) cm(6) s(-1) for T = 200-400 K. By co mparison to other tropospheric oxidation reactions of thiyl radicals, addition to oxygen yields the shortest lifetime, although the low G2 S -0 bond dissociation enthalpy implies a small equilibrium constant and means that HSOO formation is likely to be important only below 298 K. Singlet and triplet SOO have been characterized, and Delta H-f,H-298( (SOO)-S-1) is predicted to be 185.5 kT mol(-1) The results are discuss ed in the context of atmospheric chemistry.