Vibrational Relaxation of SCH sub 3 on Silver

We report time-domain measurements of vibrational relaxation for asymmetric methyl stretching modes of dimethyl disulphide dissociatively adsorbed to Ag(111). The experiments are done using transient sum frequency generation with picosecond resolution. The observed energy relaxation times (3 ps and 65 ps) are too fast to be primarily due to electron-hole damping by the metal. A mechanism where the initial energy redistribution is intramolecular is the only one consistent with the temperature dependence of the measured dynamics, and we propose a specific microscopic pathway for the relaxation.