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 k1 (297 K) = (1.01 ± 0.15) × 10-10 cm3 molecule-1 s-1 is similar to a value reported by Balla et al. and approximately 50% greater than other previously reported values; listed errors represent 95% confidence limits. Reaction 1 has a negative activation energy: k1 = (4.3 ± 1.3) × 10-11 exp[(240 ± 100)/T] cm3 molecule-1 s-1 for T = 222−420 K. Reaction 2 has a rate coefficient similar to reaction 1 at room temperature: k2 (296 K) = (1.05 ± 0.16) × 10-10 cm3 molecule-1 s-1 but has a small positive activation energy with k2 = (2.4 ± 0.7) × 10-10 exp[−(210 ± 80)/T] cm3 molecule-1 s-1 for T = 223−402 K. The temperature dependence of k2 is determined for the first time. Reactions of NO2 with HS, CH3S, and C2H5S are compared.