Vibrational relaxation and frequencies of liquid molecules. I. Theoretical expressions for practical calculation

Abstract On the basis of the generalized Langevin equation, Raman isotropic band widths and frequencies of liquid molecules have been given as functions of various physical properties of solute and solvent molecules, all of which can be measured or estimated in a reasonable way. The theory involves all three types of vibrational relaxation processes, i.e. energy dissipation, phase modulation, and resonant energy exchange, and allows for the dipole-dipole, the dispersion, and the atom-atom collision potential in their practical form. The resulting expression has made it practical, for the first time, to estimate and compare the contributions of the three relaxation processes and intermolecular potentials to the band widths and the frequency shifts.