ATMOSPHERIC CHEMISTRY OF DIMETHYL SULFIDE - UV SPECTRA AND SELF-REACTION KINETICS OF CH3SCH2 AND CH3SCH2O2 RADICALS AND KINETICS OF THE REACTIONS CH3SCH2-]CH3SCH2O2 AND CH3SCH2O2+NO-]CH3SCH2O+NO2(O2)

A pulse radiolysis technique has been used to measure the UV spectra o f CH3SCH2 and CH3SCH2O2 radicals over the range 225-350 nm. At 285 nm, sigma(CH3SCH2) = (9.8 +/- 1.7) x 10(-18); at 250 nm, sigma(CH3SCH2O2) = (4.3 +/- 0.7) x 10(-18) cm2 molecule-1. Observed self-reaction rate constants, defined as -d[CH3SCH2]/dt = 2k6[CH3SCH2]2 and -d[CH3sCH2O2 [/dt = 2k7obs[CH3SCH2O2]2, were k6 = (3.0 +/- 0.6) x 10(-11) and k7obs . = (7.9 +/- 1.4) x 10(-12) cm3 molecule-1 s-1. Errors are statistical (2 standard deviations) plus our estimate of potential systematic unc ertainty (15%). A rate constant, k2 = (5.7 +/- 0.4) X 10(-12) cm3 mole cule-1 S-1, was derived for the addition reaction CH3SCH2 + O2 --> CH3 SCH2O2. A rate constant, k3 = (1.9 +/- 0.6) x 10(-11) cm3 molecule-1 s -1, is reported for the reaction of CH3SCH2O2 radicals with NO, produc ing NO2. Errors for k2 and k3 are 2 standard deviations. Results are d iscussed with respect to the atmospheric chemistry of dimethyl sulfide .