Temperature dependence of rate coefficients of reactions of NO2 with CH3S and C2H5S

Abstract

Rate coefficients of reactions (1) CH3S + NO2 and (2) C2H5S + NO2 were determined using laser photolysis and laser-induced fluorescence, CH3S and C2H5S radicals were generated on photolysis of CH3SSCH3 and C2H5SSC2H5, respectively, with a KrF excimer laser at 248 nm. Their concentrations were monitored via fluorescence excited by emission from a dye laser at 371.4 nm (for CH3S) or 410.3 nm (for C2H5S) pumped with a pulsed XeCl excimer laser at 308 nm. Our measurements show that k(1) (297 K) = (1.01 +/- 0.15) x 10(-10) cm(3) molccule(-1) s(-1) is similar to a value reported by Balla ct al. and approximately 50% greater than other previously reported values; listed errors represent 95% confidence limits. Reaction 1 has a negative activation energy: k(1) = (4.3 +/- 1.3) x 10(-11) exp[(240 +/- 100)/T] cm(3) molecule(-1) s(-1) for T = 222-420 K. Reaction 2 has a rate coefficient similar to reaction 1 at room temperature: k(2)(296 K) = (1.05 +/- 0.16) x 10(-10) cm(3) molecule(-1) s(-1) but has a small positive activation energy with k(2) = (2.4 +/- 0.7) x 10(-10) exp[(-210 +/- 80)/T] cm(3) molecule(-1) s(-1) for T = 223-402 K. The temperature dependence of k(2) is determined for the first time. Reactions of NO2 with HS, CH3S, and C2H5S are compared.