Vibrational bandshape analysis and inertial-stochastic molecular motion in anisotropic ordered fluids

We generalize the extended J-diffusion model to molecular reorientational dynamics in uniaxially aligned fluids such as nematics. In particular we calculate correlation functions valid for both the inertial and stochastic regimes of the motion. Such functions are then used to fit correlation functions determined experimentally from Infrared and Raman bandshape analysis. We determined thus the parameters of the model, namely the molecular moments of inertia, the spinning and tumbling diffusion coefficients, the angular momentum correlation time and the average rotation angle in the inertial phase of the molecular motion. The results confirm the validity of the extended J-model for the rotational dynamics in anisotropic fluids, and provide the first direct experimental verification of the validity of the small-step diffusion model to describe the stochastic regime. J. Physique 48 (1987) 457-463 MARS 1987,