Time-resolved optical Kerr effect experiments on supercooled benzene and test of mode-coupling theory

Abstract

We have performed time-resolved optical Kerr effect experiments with heterodyne detection on benzene. We succeeded in supercooling benzene by 21 K below the melting point T _m = 279 K, and we investigated the full range of existence from the supercooled phase up to the boiling point T _b = 353 K. Our time-resolved data show clearly the complex relaxation pattern of benzene that is characterized by different time scales. These dynamic features, common to many other molecular liquids, to date have not been addressed and there is not a unique theoretical model able to explain them, even in a simple molecular liquid such as benzene. We compare our data with the predictions of a schematic mode-coupling model, fitting the experimental relaxations with a numerical solution of the time-dependent correlation functions. Although the temperature range investigated is clearly outside the asymptotic scaling regime, we found the mode-coupling model able to describe properly the measured dynamics in large time and temperature ranges.

Acknowledgements

We thank R. Righini and J. Wuttke. This work was supported by Istituto Nazionale per la Fisica della Materia, Ministero della Istruzione, dell’Università e della Ricerca (MIUR) (COFIN 2002) and EC grant N.HPRI-CT1999-00111. S. Wiebel thanks the Marie Curie Training Inside Program of the EC (contract HPMT2000-00123) for a fellowship.