MECHANISM OF THE NO3+DMS REACTION BY DISCHARGE FLOW MASS-SPECTROMETRY

The reaction of NO3 and dimethyl sulfide (DMS) has been studied at 298 K and 1 Torr pressure using the discharge flow mass spectrometric technique. Chemical titration of the primary radical produced by Br-2 and Cl-2 has shown that the reaction proceeds predominantly through NO3 + CH3SCH3 --> CH3SCH2 + HNO3 (1), the alternative channel yielding CH3 and CH3SONO2 being less than 2%. From the kinetic analysis of the NO3/DMS/Br-2 system the rate constant of the secondary reaction NO3 + CH3SCH2 --> products (9) was found to be k(9) similar to 3 x 10(-10) cm(3) molecule(-1) s(-1). Addition of O-2 to the NO3 + DMS + Br-2 and NO3 + DMS + Cl-2 systems led to determination of the rate constant of the addition reaction CH3SCH2 + O-2 + M --> CH3SCH2O2 + M (14): k(14) similar to 2 X 10(-13) cm(3) molecule(-1) s(-1) at 1 Torr of helium, The CH3SCH2O2 adduct was detected by mass spectrometry. Mass spectral identification of products gave information on the further steps of the mechanism. The CH3SCH2O radical was found to decompose to CH3S and CH2O and also to react with O-2 to give CH3SCHO and HO2 under the experimental conditions of the study.