Vibrational relaxation in condensed media

We review the literature on spectroscopic methods of studying processes of vibrational relaxation of molecules in condensed media; special attention is paid to liquids. We discuss the features and advantages of the following methods: spontaneous Raman scattering, picosecond spectroscopy, and active Raman spectroscopy. Comparison of the results obtained by the different methods yields detailed information on the course of relaxation processes.