The mechanisms, energetics, and kinetics of the gas-phase reactions of terrestrial plant-derived dimethyl thiosulfinate (DMTS) with the atmospheric oxidants OH and Cl radicals were investigated using high-level ab initio calculations. The results show that the addition of OH and Cl radicals to the sulfinyl [-S(=O)] of DMTS, followed by S(=O)-S single bond cleavage to form methanesulfinic acid + CH3S center dot and methanesulfinyl chloride + CH3S center dot, respectively, are the more dominant reactions. The barrier heights for the reactions with OH and Cl radicals were found to be -5.6 and -12.7 kcal/mol relative to the energies of the starting reactants, respectively, when computed at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311++G(3df,3pd) level of theory. The rate constants for all possible pathways of DMTS + (OH)-O-center dot/Cl-center dot reactions were investigated using the MESMER kinetics code over the temperature range between 200 and 300 K. The calculated global rate constants for the DMTS + (OH)-O-center dot and DMTS + Cl-center dot reactions at 300 K were found to be 1.42 x 10(-11) and 3.72 x 10(-11) cm(3) molecule(-1) s(-1), respectively. In addition, the thermochemistry of all possible paths and branching ratios was determined. The atmospheric chemistry implications of the DMTS + (OH)-O-center dot/Cl-center dot reactions are discussed.