INTERMOLECULAR TRANSLATIONAL-ROTATIONAL CONTRIBUTION TO NUCLEAR-SPIN RELAXATION IN LIQUIDS

The intermolecular contribution to spin relaxation by translational-rotational diffusion dynamics in molecular liquids is calculated for arbitrary relative time scales of the two stochastic processes. The resulting relaxation times are functions of variables that are proportional to ratios between rotational and translational diffusion constants, in substantial generalization of earlier theoretical approaches. In the first part the general treatment for symmetric-top molecules is given with a reduction to quadratures and a simpler version for the spherical case. In order to avoid numerical integrations an essential second part is then devoted to developing accurate analytical approximations to unsolvable integrals. For reasons of efficient and stable numefical evaluations, strong emphasis is given to an algorithmically advantageous representation of all results. A final numerical test yields excellent agreement of the results from numerical integrations with those obtained from the approximate analytical formulas over a wide range of ratios between rotational and translational diffusion constants.