THEORY OF ROTATIONAL RELAXATION IN COHERENT RAMAN-SPECTROSCOPY

The theory of the nonlinear optical processes in recent high-resolutio n coherent Raman spectroscopic studies of gases is reviewed, and a uni fied description of various spectroscopic techniques in terms of the c orrelation functions of molecular polarizability tenser is presented. A theoretical description of spectral line shapes in terms of a relaxa tion matrix, which provides the connection between the microscopic int ermolecular potential and the experimental observables, is discussed. We pay particular attention to ab initio scattering calculations start ing from accurate interaction potentials for the linewidths, line shif ts, and line-mixing parameters for the system of deuterium molecules i nteracting with a bath of inert gas atoms, under a wide range of pertu rber densities. It is clear that for simple systems involving foreign gas broadening, the theory has reached the maturity that first-princip les calculation of line spectra is highly feasible. Future directions of theoretical research from both a fundamental point of view and prac tical considerations are indicated.