Vibrational population lifetimes of polyatomic molecules in liquids

CH-stretching modes were first excited by picosecond infrared pulses and the generated excess population was monitored by anti-Stokes scattering of subsequent ultrashort probe pulses. Experimental data are reported on five molecules: CHCl₃, CH₂Cl₂, CH₃CCl₃, CH₃CH₂OH, and CH₃I in the neat liquid and/or in solutions of CCl₄. The observed time constants vary between 1 and 100 ps depending upon the individual molecule and surrounding. Theoretical calculations show that rotational coupling, Fermi resonance, Coriolis coupling, and resonance energy transfer can strongly effect the vibrational population lifetime. The relevance of these processes is quite different for the various molecules investigated.