Unimolecular Dissociation of the Methylsulfonyl Radical and its CH3OSO Isomer Laurie J. Butler, Department of Chemistry, The University of Chicago, Chicago, IL 60637 Sulfur-containing radicals in the troposphere play a dynamic role in the oxidation of dimethyl sulfide (DMS) to sulfur dioxide. This work investigates the unimolecular dissociation of CH3SO2, a key radical intermediate in the DMS oxidation mechanism originally proposed by A. R. Ravishankara. We also investigate the CH3OSO isomer. We use state-of-the-art molecular beam scattering and imaging techniques to generate the radicals under collision free conditions and probe the dissociation to CH3 + SO2. Our experimentally-measured dissociation barrier for CH3SO2 of 14 +/- 2 kcal/mol benchmarks the high level ab initio electronic structure calculations by K.- C. Lau. Our data on CH3OSO shows the dissociation barrier is > 10 kcal/mol higher than the endoergicity.