Laboratory measurements in the energy range 0.02–1 eV of the rate constants of ion–molecule reactions involving CS +
Résumé
The energy dependence of the total rate constant and of the branching ratios of the reactions of CS+ with O2, H2, and CH4 have been determined in the energy range 0.02–1 eV by the drift tube mass spectrometer technique. The reaction CS++O2 proceeds through three primary steps giving OCS+, SO+, and O+2 with branching ratios of 0.7, 0.2, and 0.1, respectively, at low energy (<0.025 eV) and 0.4, 0.1, and 0.5 at high energy (0.38 eV). The secondary ions OCS+ and SO+ do not react with O2. The overall rate constant is energy independent (8±2)10−11 cm3 s−1, but the elementary steps leading to OCS+ and SO+ decrease in rate with increasing energy while the charge transfer reaction increase in rate. The reactions of CS+ with H2 and CH4 form HCS+; the first reaction is found to have an energy independent rate constant of (3.8±1)10−10 cm3 s−1 and the second has a measured rate constant which increases from 5.10−10 cm3 s−1 at the lowest energy studied (0.2 eV) to 1.10−9 cm3 s−1 at 1 eV. HCS+ does not react rapidly with H2 or CH4