Spectral moments of the rotational correlation functions for the first- and second-rank tensors of asymmetric top molecules

A method of evaluating the spectral moments Ml 2k of the rotational correlation functions for the first- and second-rank tensors of rigid asymmetric top molecules is developed. It is based on the calculation of the coefficients of a Taylor series expansion of the vector and tensor orientational correlation functions about t = 0 with the help of angular momentum theory, and is applicable to a pair intermolecular interaction potential with arbitrary dependence on the angular variables. Equations for the second (Ml 2), fourth (Ml 4), and sixth (Ml 6) spectral moments are obtained as a demonstration of the ability of the method. The results for (Ml 2) and Ml 4 coincide with previously known values and the equation for Ml 6 is new. As particular cases, the theory contains the results for classical ensembles of symmetric tops, spherical tops, and linear molecules.