KINETIC-STUDIES OF THE REACTIONS OF IO, BRO, AND CLO WITH DIMETHYLSULFIDE

The kinetics of the reactions of IO, BrO, and ClO with DMS have been investigated at 298 K and total pressures of 0.5-6.8 mbar He using the discharge flow-mass spectrometry technique to monitor the halogen oxide radicals. Rate coefficients of (8.8 +/- 2.1) x 10(-15), (2.7 +/- 0.5) x 10(-13) and (9.5 +/- 2.0) x 10(-15) cm3 molecule-1 s-1 have been obtained for the reactions of IO, BrO, and ClO with DMS, respectively. The result for IO with DMS is in good agreement with two other recent studies on this reaction but is nearly three orders of magnitude slower than two earlier studies, one of which was from this laboratory. The earlier studies are now thought to be in error because of heterogeneous and secondary chemistry occurring in the systems investigated. The rate coefficient for BrO with DMS is in excellent agreement with a previously reported preliminary value from this laboratory. However, the rate coefficient for ClO with DMS is a factor of 4 lower than our previously determined value. The new data are considered more reliable in view of the much improved experimental technique in the present study. DMSO was detected as a product in all of these reactions. A semi-quantitative determination of the DMSO yield was only possible in the case of the reaction of IO with DMS where a yield of 84 +/- 40% was found.