Translation-rotation coupling in transient grating experiments: Theoretical and experimental evidences

¹ LENS and Dipartimento di Fisica, Università di Firenze Largo E. Fermi 2, 50125 Firenze, Italy
² INFM, Unità di Firenze - Largo E. Fermi 2, 50125 Firenze, Italy
³ Dipartimento di Chimica Fisica, Università della Basilicata and INFM, Unità di Napoli - Italy
⁴ Dipartimento di Energetica Università di Firenze - via S. Marta, Firenze, Italy
⁵ PMC, UMR 7602, B.P. 77, Université P. et M. Curie 4 Place Jussieu, F-75005, Paris, France
⁶ LMDH, UMR 7603, B.P.86, Université P. et M. Curie 4 Place Jussieu, F-75005, Paris, France

Received: 2 July 2001
Accepted: 20 August 2001

Abstract

The results of a Transient Grating experiment in a supercooled molecular liquid of anisotropic molecules and its theoretical interpretation are presented. These results show the existence of two distinct dynamical contributions in the response function of this experiment, density and orientation dynamics. These dynamics can be experimentally disentangled by varying the polarisation of the probe and diffracted beams and they have been identified and measured in a Heterodyne Detected experiment performed on m-toluidine. The results of the theory show a good qualitative agreement with the measurements at all temperatures.