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

Abstract

The title reactions were studied using cavity ring-down spectroscopy in 100 Torr of N2 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 cm3 molecule-1, kforward = (5.0 ± 0.2) × 10-11 cm3 molecule-1 s-1, and kbackward = (1.2 ± 0.2) × 104 s-1 at 300 K in 100 Torr of N2. The absorption cross section of the Br−DMS adduct at 338.3 nm was σ = (1.2 ± 0.2) × 10-17 cm2 molecule-1. An upper limit of k < 1 × 10-18 cm3 molecule-1 s-1 was established for the reaction of O2 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] cm3 molecule-1 s-1 (k = 4.2 × 10-13 cm3 molecule-1 s-1 at 298 K). The uncertainties are 2 standard deviations from regression analyses.