Picosecond Time-Resolved Measurements of Vibrational Energy Transfer and Relaxation Phenomena in Large Polyatomic Molecules

Vibrational modes in the electronic ground state are investigated by recently developed ultrashort measuring techniques. Using tunable infrared pulses well defined vibrational states are first excited far above the thermal equilibrium value, and with delayed probe pulses the instantaneous population of various vibrational states is monitored. Rapid redistribution (lxlO^-12sec) between neighboring energy states is seen in various molecules while the decay to lower vibrational levels is found to depend very strongly on the mode structure of the individual molecule. Population lifetimes of 1 psec and 40 psec are measured for CH₃ modes in CH₃I and ethanol, respectively.