A many-body stochastic approach to rotational motions in liquids: complex decay times in highly viscous fluids *

Reorientational relaxation in complex liquids is still lacking a unified treatment that is capable of dealing with the relevant stochastic processes without excessive complications. A significant challenge is offered by the study of highly viscous, glassy and supercooled liquids. Rotational relaxation of flexible short chain and small rigid molecules in supercooled organic liquids have been studied in the past by researchers including Johari [ 1,2] and Williams [ 3,4]. Typical systems considered were CH2Cl, and C6HSCl in cis-decaline. More recently, Nozaky and Mashimo [ 5 ] have described a series of results on the dielectric friction of polyvinylacetate over a large range of frequencies. Supercooled liquids with highly anisotropic interactions, mainly due to hydrogen bonding (alcohols and water ) have been studied by Floriano and Angel1 [ 6 1. Magnetic resonance techniques have been applied to the study of relaxation processes in glassy systems. This includes the deuterium NMR study by Dries et al. of the glass transition in toluene, polystyrene and supercooled orthophenyl [ 7 1. It provided spin relaxation times ( T, and r,) and spin-alignment data that yield accurate in-