Critical influences on the rate of intramolecular vibrational redistribution: a comparative study of toluene, toluene-d3 and p-fluorotoluene

The intramolecular vibrational redistribution (IVR) dynamics following the excitation of a mode in the first electronically excited states of toluene, toluene-d(3) and p-fluorotoluene that has predominantly C-CH3 stretching character and an internal energy of similar to 1200 cm(-1) have been compared using picosecond time-resolved photoelectron imaging spectroscopy as a probe. Temporal changes in the intensities of spectral features in each molecule have enabled IVR lifetimes of 12, 15 and 50 ps, respectively, to be determined. Our measurements show that doorway states are critical in mediating the IVR dynamics in toluene and toluene-d(3), and we deduce that these doorway states, which are assigned in the course of this work, are also instrumental in reducing the IVR lifetimes of these molecules relative to p-fluorotoluene.