Study of the dissociation of CH3SCH3+ by collisional activation : Evidence of nonstatistical behavior

The collision-induced dissociation (CID) reaction of CH₃SCH₃⁺ + Ar was studied in a triple-quadrupole, double-octopole ion-molecule reaction apparatus. The absolute total cross sections for the product ions CH₂SH⁺/CH₃S⁺, CH₂S⁺, CHS⁺, and CH₃⁺ formed in the CID reaction have been measured in the center-of-mass kinetic energy (E_cm) range of 1-19 eV. Using the charge-transfer probing technique, we found that mass-47 product ions are formed in both the CH₂SH⁺ and CH₃S⁺ structures. The onsets for CH₂SH⁺, CH₃S⁺, CH₂S⁺, CHS⁺, and CH₃⁺ are consistent with their thermochemical thresholds. The formation of the higher-energy product channel CH₃S⁺ + CH₃, which involves C-S bond scission, is found to dominate in the E_cm range immediately above its onset. The lower-energy channel corresponding to the formation CH₃SCH₂⁺ + H is not found. The strong preference observed for the higher-energy channel is in accordance with the conclusions obtained from the CID studies of CH₃SH⁺ and CH₃CH₂SH⁺, providing further evidence that the CID of CH₃SCH₃⁺ is also nonstatistical. The high yield of CH₃S⁺ + CH₃ is attributed to the more efficient translational-to-vibrational energy transfer for the C-S stretching modes with lower frequencies than to those for the C-H stretching modes with higher frequencies, along with weak coupling between these vibrational modes with significantly different frequencies of CH₃SCH₃⁺. In addition, the dissociation pathways deduced are consistent with the results of ab initio calculations at the G3 level.