LOCAL ORDER EFFECT ON MOLECULAR ORIENTATIONAL DYNAMICS - TIME-RESOLVED NONLINEAR SPECTROSCOPY

We have investigated the orientational relaxation in the isotropic pha se of a liquid crystal (ZLI-1167) and in the liquid phase of the p-ter phenyl (pTP) and p-quater-phenyl (pQP) molecules. The experimental res ults show new aspects of the liquid molecular orientational dynamics c ommon to all three systems, independently from their chemical nature a nd state of aggregation. They are characterised by slow collective dyn amics in good agreement with the Landau-de Gennes theory of phase tran sition and by a fast dynamics in fair agreement with the Debye diffusi ve theory. These new aspects are shown to be related to local order ef fects.