FTIR Kinetic and Mechanistic Study of the Atmospheric Chemistry of Methyl Thiolformate

Abstract

Some aspects of the atmospheric chemistry of methyl thiolformate (CH 3 SCHO), a recently detected intermediate in the oxidation of dimethyl sulfide, have been investigated at 298 K and 1000 mbar total pressure in large reaction chambers using long path in situ FTIR absorption spectroscopy for the analysis. Rate coefficients of (1.11 ( 0.22) × 10 -11 and (5.80 ( 0.80) × 10 -11 cm 3 molecule -1 s -1 have been determined for its reaction with OH radicals and Cl atoms, respectively. The UV spectrum of CH 3 SCHO has been measured in the range 220-355 nm and a lower limit of 5.4 days determined for its atmospheric photolytic lifetime. Detailed product analyses have made for the OH and Cl initiated photooxidation of CH 3 SCHO. Strong SO absorption bands observed in both systems are tentatively assigned to CH 3 SOCHO in the OH system and to CH 3 SOCl in the Cl system. The first gas-phase spectra of CH 3 SCl and CH 3 SOCl are also presented. The results are discussed with respect to the atmospheric chemistry of CH 3 SCHO and possible consequences for the photooxidation mechanism of dimethyl sulfide.

FT-IR product study of the photo-oxidation of dimethyl sulfide: Temperature and O2 partial pressure dependence

“…With the exception of methyl thiolformate all the chemicals employed were commercial products and were used without further puriÐcation. Methyl thiolformate was synthesised as described in Patroescu et al 25 and had a GC purity of [98%.…”

Theoretical spectroscopic characterization at low temperatures of S-methyl thioformate and O-methyl thioformate

“…21,22 MSCHO is produced by reactions of dimethyl sulfide (DMS) with the OH and NO 3 radicals. 23 Since DMS is the major biogenic source released to the atmosphere, MSCHO can be considered a species of significant atmospheric importance. Its isomer, Omethyl thioformate (CH 3 terized species whose applications are not noticeable.…”

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

“…The infrared spectrum of CH 3 SBr was obtained by the 254-nm photolysis of dimethyl disulfide with molecular bromine in 1000 mbar of N 2 . A similar process using the photolysis of DMDS in the presence of Cl 2 has recently been used to produce CH 3 SCl in close to unit yield [28]. The infrared absorption bands obtained for CH 3 SBr are listed in CH S ϩ Br ϩ M !…”

“…From the absorptions listed in Table III, contributions from methanesulfinyl bromide (CH 3 SOBr) and sulfuryl bromide (SOBr 2 ) are possibilities. The further oxidation of CH 3 SCl is known to lead to the chlorinated analogs [28]. Figure 3 shows an example of the concentrationtime profiles for DMS and the identified products during the photolysis of molecular bromine and DMS in 1000 mbar of synthetic air (i.e., 200 mbar O 2 ).…”