MULTIDIMENSIONAL FEMTOSECOND SPECTROSCOPIES OF VIBRATIONAL MOTIONS INLIQUIDS - SEMICLASSICAL EXPANSION

Fifth- (chi((5))) and seventh-(chi((7))) Older electronically off-reso nant Raman spectroscopies-in molecular liquids are investigated using a new semiclassical expansion of the optical response which applies fo r weak anharmonicities and low temperatures. The leading contribution can be calculated using classical equations of motion for nuclear wave packets, even when the system itself may be highly nonclassical. Two sources of nonlinearities which generate the signals-the nonlinear dep endence of the polarizability on nuclear coordinates and vibrational a nharmonicities-are identified. Formal analogy between the present equa tions and the time-dependent Hartree-Fock equations used in electronic nonlinear spectroscopy suggests specific experimental signatures of t he various nonlinearities. (C) 1998 American Institute of Physics.