Novel information about vibrational relaxation in liquids using time-resolved stokes probing after picosecond IR excitation

The use of Stokes difference spectra for picosecond studies of vibrational relaxation dynamics in condensed matter is introduced and compared to the established techniques of measuring anti-Stokes scattering or IR transmission changes. A simple quantum mechanical description reveals the principal similarities and differences of the different probing processes for the case of moderately anharmonic oscillators, e.g., Liquids with only relatively weak interactions of the sample molecules. The outcome is illustrated by novel experiments on neat liquid chloroform, whose relaxation is known quite well. It is shown that transient Stokes data allow additional information, particularly about the behavior of low-lying vibrational levels and the type of energy transfer during relaxation, to be obtained.