RANK DEPENDENCE OF ORIENTATIONAL RELAXATION IN DIPOLAR SYSTEMS

An important yet unsolved problem in the field of orientational relaxa tion in dipolar liquids is the dependence of the correlation functions C(l)(t), C(l)(t) = [4pi/(2l + 1)SIGMA(m = -l)l [Y(lm)(OMEGA(0)Y(lm)(O MEGA(t))] on the rank l (where Y(lm)(OMEGA) are the usual spherical ha rmonics). The existing theories on this effect differ in their predict ions. To investigate this, we have carried out extensive computer simu lations of a Brownian dipolar lattice. The dielectric friction was fou nd to decrease rapidly with increasing l, in qualitative agreement wit h the predictions of Hubbard-Wolynes. However, the observed effect is much stronger than the predictions of the existing theories.