PRETRANSITIONAL EFFECTS IN THE LIQUID PLASTIC PHASE-TRANSITION OF P-TERPHENYL

A study of the orientational dynamics of liquid p-terphenyl in the tim e domain by means of transient optical Kerr effect spectroscopy is pre sented. The orientational relaxation is measured at several temperatur es above the liquid-plastic phase transition, following the decay from a few hundreds of fs to about 700 ps. Pre-transitional effects are ob served above the phase transition. Approaching the transition temperat ure, a bifurcation of the orientational relaxation times is present. T he faster orientational time follows the Debye-Stokes-Einstein hydrody namic theory up to the phase transition without any critical effect. T he slower time shows a typical critical slowing down, in agreement wit h the Landau-de Gennes theory of first-order phase transitions.