Classical dynamics study of the unimolecular decomposition of CH3SH+

The dynamics of three decomposition channels of the mercapto cation (CH3SH) were investigated by classical trajectories and RRKM formalisms. The thre e channels are (I) CH bond dissociation through a "tight" transition state, (II) CS bond cleavage, and (I:II) SH bond scission. These calculations wer e performed with an analytical potential energy surface constructed from th eoretical and experimental data available in the literature. The relative y ields of CH3+ and CH2SH+ products are in qualitative agreement with charge- exchange experiments. The dynamical calculations revealed that the system i s intrinsically non-Rice-Ramsperger-Kassel-Marcus (RRKM) at the energies se lected in this study. Under nonrandom initial conditions, the system showed strong mode specificity, which may be rationalized by weak couplings betwe en the low- and high-frequency modes, particularly the CH3 stretching norma l modes, which is consistent with collisional activation studies. The class ical trajectory calculations revealed an inverse isotope effect for both th e CS and SH scission channels and a normal isotope effect for the CH bond d issociation process. Finally, we have found that molecular rotation decreas es the mercapto cation decomposition rate and that orbital angular momentum dramatically modifies the relative yields of CH3+ and CH2SH+ products.