Europhys. Lett, 43 (5), pp. 546-551 (1998)

Light scattering by low-frequency excitations in
quasi-periodic n-alkane/urea adducts

J. Ollivier ¹, C. Ecolivet ¹, S. Beaufils ¹, F. Guillaume ² and T. Breczewski ³

¹ Groupe Matière Condensée et Matériaux, URA CNRS 804, Université de Rennes I
Campus de Beaulieu, Rennes 35042, France
² Laboratoire de Spectroscopie Moléculaire et Cristalline, URA CNRS 124
Université de Bordeaux 1 - 351 cours de la Libération, 33405 Talence cedex, France
³ Departemento de Física de la Materia Condensada, Facultad de Ciencias
Universidad del Pais Vasco - Apdo 644, Bilbao, Spain

(received 30 April 1998; accepted 13 July 1998)

PACS. 61.44Fw - Incommensurate crystals.
PACS. 63.20 - Phonons in crystal lattices.
PACS. 78.35 - Brillouin and Rayleigh scattering; other light scattering.

Abstract:

High-resolution light scattering spectroscopy has been performed on a series of n-alkane /urea inclusion compounds with . The elastic constants of these incommensurate composite crystals have been determined and found to be independent of the chain length of the guest molecules. In addition, no extraneous acoustic-like mode appeared in all spectra. However, quasi-elastic components with different widths are observed for different polarizations. In one of them the characteristics of the scattered light suggest that the quasi-elastic broadening could be generated by a sliding mode, whereas the other detected component is assigned to the reorientational motions of the n-alkane chains about their long axis.

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