VIBRATIONALLY RESOLVED TRANSLATIONAL ENERGY-RELEASE SPECTRA FROM THE ULTRAVIOLET PHOTODISSOCIATION OF METHYL MERCAPTAN

Product translational energy release spectra resulting from 248 and 19 3 nm photodissociation of methyl mercaptan are obtained for the hydrog en atom channels (CH3SH+hnu-->CH3S+H) by using the high-n Rydberg time -of-flight technique. The spectra exhibit vibrational structure that i s 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 a re populated. The progression observed at 193 nm is bimodal, with the higher kinetic energy component showing greater spatial anisotropy tha n the lower energy component, suggesting that two different processes occurring on different time scales are responsible for the two compone nts. The results at 248 nm are consistent with excitation to a repulsi ve electronic surface. For 193 nm excitation, the high kinetic energy component is consistent with direct photoexcitation to a repulsive sur face and/or rapid intramolecular access to a repulsive surface. The lo wer kinetic energy component presumably derives from the molecule spen ding more time on an excited surface. A simple model is applied to est imate the extent of C-S bond extension for the various processes.