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 pres sure range 1-612 Torr of He using laser pulsed photolysislaser-induced fluo rescence and discharge now mass spectrometry/laser-induced fluorescence tec hniques. The upper limit for the thermal decomposition rate of CH3SO2 in th e 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 calculat ions. The CH3SO2 decomposition rate at 760 Torr and 300 K has been estimate d 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 f or 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 basi s of ab initio and RRKM calculations, the experimental results have been in terpreted by assuming the reaction of CH3SO with NO2 to form chemically act ivated CH3SO2* radical followed by its thermal stabilization or prompt deco mposition to CH3 and SO2. The implication of the obtained results for the a tmospheric oxidation of dimethyl sulfide is discussed.