RELAXATION OF A MOLECULAR GLASS AT INTERMEDIATE TIMES

The results of a detailed molecular-dynamics investigation of relaxati on in the van der Waals system o-terphenyl are presented. Our calculat ions give evidence for the existence of a fast process on the picoseco nd timescale. This confirms the neutron-scattering observation of an a nomalous decrease of the Debye-Waller factor, predicted by mode-coupli ng theory, and reconciles it with the temperature-independent process with a 3 ps relaxation time observed in light-scattering experiments. We demonstrate that this process results from the strongly anharmonic motion of molecules trapped in the cages formed by their neighbours.