TIME-RESOLVED ANISOTROPIC COHERENT ANTI-STOKES-RAMAN SCATTERING - A NEW PROBE OF REORIENTATIONAL DYNAMICS

A formalism for the time-dependent anisotropic third-order susceptibil ity induced by a linearly polarized excitation pulse has been derived to describe the time dependence of coherent anti-Stokes Raman scattere d (CARS) and Raman time-resolved experiments. The third-order suscepti bility induced in a randomly oriented molecular system contains nine i ndependent molecular parameters-three isotropic and six anisotropic-as compared to three independent parameters in an isotropic system. Meth ods of time-resolved anisotropic anti-Stokes Raman scattering (TRA CAR S) are discussed as an approach to reorientational measurements. The d ependence of the TRA CARS or TRA Raman signal on vibration and polariz ation component can in principle provide more rotational information t han fluorescence depolarization or linear dichroism measurements and m ay allow more complete characterization of rotational dynamics. Result s are reported for three types of TRA CARS experiments to demonstrate the capabilities of TRA CARS to study the rotational motion of molecul es in liquids.