Absolute rate parameters for the reaction of ground state atomic oxygen with dimethyl sulfide and episulfide

Absolute rate constants for the reactions of O(3P) atoms with dimethyl sulfide and episulfide have been measured over the temperature range 268 to 424 °K. The kinetic data were obtained using the flash photolysis–resonance fluorescence method. The O(3P)+CH3SCH3 reaction exhibited a negative temperature dependence and the Arrhenius expression obtained was k1= (1.42±0.07) ×10−11 exp(727±31/RT) cm3 molecule−1⋅sec−1. The episulfide reaction was essentially temperature independent, the corresponding Arrhenius expression being k2= (1.34±0.09) ×10−11 exp(−35±40/RT) cm3 molecule−1⋅sec−1. Use of a fast flow system with direct mass spectrometric analysis of reaction products provides evidence that the reaction mechanisms involved are O(3P)+CH3SCH3⇄[CH3SOCH3]*→CH3SO+CH3, O(3P)+CH2–SCH2⇄[CH2–SOCH2]*→CH2=CH2+SO. The very great difference in reaction rates and mechanisms between these sulfides and the corresponding oxygen analogs CH3OCH3 and ethylene oxide is discussed.