Vibrationally resolved translational energy release spectra from the ultraviolet photodissociation of methyl mercaptan

Abstract

Product translational energy release spectra resulting from 248 and 193 nm photodissociation of methyl mercaptan are obtained for the hydrogen atom channels (CH3SH+hν→CH3S+H) by using the high-n Rydberg time-of-flight technique. The spectra exhibit vibrational structure that is assigned to a CH3–S stretch progression. At 248 nm, the progression extends only to v=2, while at 193 nm levels up to approximately v=17 are populated. The progression observed at 193 nm is bimodal, with the higher kinetic energy component showing greater spatial anisotropy than the lower energy component, suggesting that two different processes occurring on different time scales are responsible for the two components. The results at 248 nm are consistent with excitation to a repulsive electronic surface. For 193 nm excitation, the high kinetic energy component is consistent with direct photoexcitation to a repulsive surface and/or rapid intramolecular access to a repulsive surface. The lower kinetic energy component presumably derives from the molecule spending more time on an excited surface. A simple model is applied to estimate the extent of C–S bond extension for the various processes.