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

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.