The unimolecular dissociation of methanethiol cation (CH3SH+, 1) has been investigated theoretically. Ab initio and Gaussian-2 theory calculations have been performed to obtain the potential energy surface (PES) for loss of H and H-2 from 1. On the basis of the PES obtained, the relative abundances of the two channels near threshold have been calculated by Rice-Ramsperger-Kassel-Marcus modeling. The calculated result agrees with the previous experimental one, suggesting that the dissociation occurs statistically near threshold on the ground electronic state. (c) 2006 Elsevier B.V. All rights reserved.