Coherent Raman Spectroscopy.

The nonlinear Raman scattering is discussed as a potential probe for the study of radicals, ions and Van der Waales pairs of rare gases. Significant progress in developing these new Raman techniques is reported. The new approach has been developed in our laboratory for measuring small gains in a pulsed probe laser, which combined with polarization techniques gives improvements in the sensitivity of Raman gain spectroscopy, and show the feasibility for obtaining spectra at partial densities as low as 10('12) molecules cm('-3). Theoretical calculation of the complete nonlinear Raman spectrum of argon dimers is presented. Both quantum mechanical and classical approaches are applied. It is shown that classical line shape can simulate very closely quantum mechanical one if proper correction to classical pair distribution function are applied.