Mechanism of the reaction of CH3SO with NO2 in relation to atmospheric oxidation of dimethyl sulfide:: Experimental and theoretical study

CH3SO2 radical decomposition and the mechanism of SO2 and CH3 formation in the reaction of CH3SO with NO2 were experimentally investigated in the pressure range 1-612 Torr of He using laser pulsed photolysislaser-induced fluorescence and discharge now mass spectrometry/laser-induced fluorescence techniques. The upper limit for the thermal decomposition rate of CH3SO2 in the investigated pressure range has been found to be 100 s(-1) at 300 K. High-pressure limit, k(infinity) = 2.08 x 10(3) s(-1), and low-pressure limit, k(0) = 2.72 x 10(-17) cm(3) molecule(-1) s(-1), of the rate coefficient of the CH3SO2 decomposition have been derived from ab initio and RRKM calculations. The CH3SO2 decomposition rate at 760 Torr and 300 K has been estimated to be about 200 s(-1) from falloff calculations. Reaction of CH(3)So with NO2 has been found to form CH3 and SO2 with a yield varying from (0.33 +/- 0.05) at 13 Torr to (0.18 +/- 0.03) at 612 Torr of He. The rate constant for the reaction of CH3SO with NO2 has been found to be (1.5 +/- 0.4) x 10(-11) cm(3) molecule(-1) s(-1) at 300 K, independent of pressure. On the basis of ab initio and RRKM calculations, the experimental results have been interpreted by assuming the reaction of CH3SO with NO2 to form chemically activated CH3SO2* radical followed by its thermal stabilization or prompt decomposition to CH3 and SO2. The implication of the obtained results for the atmospheric oxidation of dimethyl sulfide is discussed.