KINETICS AND MECHANISMS OF THE REACTIONS OF CH3S, CH3SO, AND CH3SS WITH O3 AT 300-K AND LOW-PRESSURES

The reactions of CH3S + O3 --> products (1), CH3SO + O3 --> products (2), and CH3SS + O3 --> products (3) were investigated at 300 K in a discharge flow tube reactor coupled to a photoionization mass spectrometer. The measured value of k1 is (5.7 +/- 1.4) x 10(-12) cm3 molecule-1 s-1 in 1 Torr He. We observed that OH was produced in this reaction or in subsequent steps and that complex branched chain reactions, which generate CH3S from its precursor molecule, took place in our flow tube reactor. We found that CH3SO was a product of reaction 1 and the branching ratio for this channel was 15 +/- 4%, between 0.7 and 2.2 Torr He, independent of pressure. A preliminary value of k2 = (6 +/- 3) x 10(-13) cm3 molecule-1 s-1 was measured. CH3S was not a major product of reaction 2. These results suggest that the reaction with O3 is a major CH3S removal process in the atmosphere. The rate coefficient for the reaction of CH3SS with O3 (3) was measured to be k3 = (4.6 +/- 1.1) x 10(-13) cm3 molecule-1 s-1.