Vibration Mediated Photodissociation Dynamics of CH3SH: Manipulation of the Dynamic Energy Disposal into Products

Abstract

The S-H bond dissociation dynamics of CH3SH have been investigated for the S-1-S(0)transition mediated by either the S-H stretching (2608 cm(-1)) or CH(3)symmetric stretching (2951 cm(-1)) mode excitation in the S(0)state. The S-H and C-S bond extensions are strongly coupled in the S(1)state through the S-1/S(2)same-symmetry conical intersection, giving the C-S stretching mode excitation of the CH3S fragment during the prompt S-H bond rupture on S-1. In the IR + UV transition mediated by the S-H stretching mode, the vertical transition seems to access the Franck-Condon region where the S-H bond is shortened while the coupling to the C-S bond stretching becomes stronger compared to the case of one-photon UV transition, indicating that the intramolecular vibrational redistribution (IVR) is little activated in S-0. When the IR + UV excitation is mediated by the CH(3)symmetric stretching mode, on the other hand, the Franck-Condon region in S(1)encompasses the enlarged molecular structures with respect to both S-H and C-S bond extensions, presumably due to the rapid IVR in S(0)prior to the vertical transition. This leads to the inverted vibrational state population of the C-S bond stretching mode of the CH3S fragment. This work demonstrates that the reaction dynamics upon the IR + UV excitation of CH3SH is highly mode dependent and the energy disposal dynamics could be controlled by the manipulation of the Franck-Condon region through the particular vibrational-state mediation in the ground state, shedding new light on the structure-dynamics relationship.