Vibrational energy redistribution in liquid benzene

Ultrafast anti-Stokes Raman spectroscopy after mid-IR excitation of a C-H stretching transition is used to study vibrational energy relaxation (VER) and vibrational cooling (VC) of liquid benzene. By adding CCl₄ to benzene and monitoring the CCl₄ Raman transitions, the time-dependence of energy build-up in the bath was measured, which showed that VC in benzene occurs about 10 times slower than the 8 ps decay of the C-H stretch. A surprising result is that most VER lifetimes are practically the same as in a low-temperature crystal. This result is explained by the VC model of Hill and Dlott (J. Chem. Phys. 89 (1988) 830).