Vibrational origin of the fast relaxation processes in molecular glass formers

¹ Center for Polymer Studies and Department of Physics Boston University, Boston, MA 02215, USA
² Dipartimento di Fisica and INFM, Università di Roma “La Sapienza" Piazzale Aldo Moro 2, Roma, I-00185, Italy
³ European Synchrotron Radiation Facility BP 220 Grenoble Cedex, F-38043, France

Received: 19 December 2001
Accepted: 12 July 2002

Abstract

We study the interaction of the relaxation processes with the density fluctuations by molecular dynamics simulation of a flexible molecular model for o-terphenyl in the liquid and supercooled phases. We find evidence, besides the structural relaxation, of a secondary vibrational relaxation whose characteristic time, few ps, is slightly temperature dependent. This i) confirms the result by Monaco et al. (Phys. Rev. E, 62 (2000) 7595) of the vibrational nature of the fast relaxation observed in Brillouin Light Scattering experiments in o-terphenyl; and ii) poses a caveat on the interpretation of the BLS spectra of molecular systems in terms of a purely center-of-mass dynamics.