FT-IR kinetic and product study of the Br-initiated oxidation of dimethyl sulfide

Abstract

An FT-IR kinetic and product study of the Br-atom-initiated oxidation of dimethyl sulfide (DMS) has been performed in a large-volume reaction chamber at 298 K and 1000-mbar total pressure as a function of the bath gas composition (N 2 ϩ O 2 ). In the kinetic investigations using the relative kinetic method, considerable scatter was observed between individual determinations of the rate coefficient, suggesting the possibility of interference from secondary chemistry in the reaction system involving dimethyl sulfoxide (DMSO) formation. Despite the experimental difficulties, an overall bimolecular rate coefficient for the reaction of Br atoms with DMS under atmospheric conditions at 298 K of Յ1 ϫ 10 Ϫ13 cm 3 molecule Ϫ1 s Ϫ1 can be deduced. The major sulfur products observed included SO 2 , CH 3 SBr, and DMSO. The kinetic observations in combination with the product studies under the conditions employed are consistent with rapid addition of Br atoms to DMS forming an adduct that mainly re-forms reactants but can also decompose unimolecularly to form CH 3 SBr and CH 3 radicals. The observed formation of DMSO is attributed to reactions of BrO radicals with DMS rather than reaction of the Br-DMS adduct with O 2 as has been previously speculated and is thought to be responsible for the variability of the measured rate coefficient. The reaction CH 3 O 2 ϩ Br : BrO ϩ CH 3 O is postulated as the source of BrO radicals.

Theoretical study on the Br + CH3SCH3 reaction

“…Table1 lists the harmonic vibrational frequencies of the reactant, HBC, products, and transition states calculated at the MP2/6‐31+G(d,p) level as well as the available experimental values 14, 35, 37–39. For the species CH 3 SCH 3 , HBr, CH 3 SBr, CH 3 , CH 3 S, and CH 3 Br, the calculated frequencies are in good agreement with the experimental values with the largest deviation of 7%.…”

“…A few experimental kinetic studies have been performed on reaction of DMS with Br atom at the 298 K and in the temperature range of 386–604 K. In a mechanism view, three channels are available for the title reaction, i.e., At 298 K, the relative overall rate constants are obtained by Ballesteros et al13 and Maurer et al14 However, only upper limit value, k ≤ 1 × 10 −13 cm 3 /(molecule s), was presented by Maurer et al14 The total rate–temperature expression of k = (9.0 ± 2.9) × 10 −11 exp[(−2386 ± 151)/ T ] cm 3 /(molecule s) over the temperature range 386–604 K was presented by Jefferson et al15 These experimental values agree well with each other in the common temperature.…”