Cavity Ring-Down Spectroscopic Study of the Reactions of Br Atoms and BrO Radicals with Dimethyl sulfide

The title reactions were studied using cavity ring-down spectroscopy in 100 Torr of N 2 diluent at 278−333 K. The equilibrium constant and rates of the forward and reverse reactions of the Br + DMS ⇄ Br−DMS equilibrium were determined to be K = (4.1 ± 0.3) × 10 -15 cm 3 molecule -1, k forward = (5.0 ± 0.2) × 10 -11 cm 3 molecule -1 s -1, and k backward = (1.2 ± 0.2) × 10 4 s -1 at 300 K in 100 Torr of N 2 . The absorption cross section of the Br−DMS adduct at 338.3 nm was σ = (1.2 ± 0.2) × 10 -17 cm 2 molecule -1 . An upper limit of k < 1 × 10 -18 cm 3 molecule -1 s -1 was established for the reaction of O 2 with the Br−DMS adduct. The kinetics of the reaction of BrO with DMS were well described by the Arrhenius expression k = (1.3 ± 0.1) × 10 -14 exp[(1033 ± 265)/ T ] cm 3 molecule -1 s -1 ( k = 4.2 × 10 -13 cm 3 molecule -1 s -1 at 298 K). The uncertainties are 2 standard deviations from regression analyses.