Dissociation of CH<INF>3</INF>SH<SUP>+</SUP> by Collisional Activation:  Evidence of Nonstatistical Behavior

We have measured the absolute total cross sections for CH<INF>2</INF>SH⁺(CH<INF>3</INF>S⁺), CH<INF>2</INF>S⁺, HCS⁺, HS⁺, CH<INF>3</INF>⁺, and CH<INF>2</INF>⁺ produced by the collision-induced dissociation (CID) reaction of CH<INF>3</INF>SH⁺(1²A‘‘) + Ar in the center-of-mass collision energy range of 1−36 eV. While the onset for CH<INF>3</INF>⁺ is consistent with the thermochemical threshold for the formation of CH<INF>3</INF>⁺ + SH, the onsets for other product ions are higher than their corresponding thermochemical thresholds. Using a charge transfer probing technique, we conclude that the m/e = 47 amu ions observed in the CID reaction have mostly the CH<INF>2</INF>SH⁺ structure. The relative yields for CH<INF>2</INF>SH⁺, CH<INF>2</INF>S⁺, HCS⁺, HS⁺, CH<INF>3</INF>⁺, and CH<INF>2</INF>⁺ formed in the CID reaction, which strongly favor the C−S bond scission process leading to the formation of CH<INF>3</INF>⁺ + SH, are significantly different from those measured in previous photoionization and charge exchange studies. Since the CH<INF>3</INF>⁺ + SH channel is not among the most stable product channels, this observation suggests that the collision-activated dissociation of CH<INF>3</INF>SH⁺ is nonstatistical. The high yield for CH<INF>3</INF>⁺ + SH observed in CID is attributed to the more efficient translational to vibrational energy transfer for the C−S stretch than for the C−H stretches of CH<INF>3</INF>SH⁺, and to weak couplings between the low-frequency C−S and the high-frequency C−H stretching vibrational modes of CH<INF>3</INF>SH⁺. The differences in excitation mechanisms for CH<INF>3</INF>SH⁺ via collision activation, photoionization, and charge exchange are responsible for the different fragment ion distributions from CH<INF>3</INF>SH⁺ observed in these experiments.