Eur. Phys. J. B 24, 51-57 (2001)
https://doi.org/10.1007/s100510170021

Dynamical molecular disorder and diffuse scattering in an alkane/urea incommensurate inclusion compound

¹ Laboratoire de Dynamique et Structure des Matériaux Moléculaires, EISA 8024, Cité Scientifique, 59655 Villeneuve d'Ascq Cedex, France
² Groupe Matière Condensée et Matériaux (UMR CNRS 6626) , Université de Rennes I, 35042 Rennes Cedex, France
³ Laboratoire de Physico-Chimie Moléculaire (UMR CNRS 5803) , Université de Bordeaux I, 33405 Talence, France
⁴ Laboratoire Léon Brillouin, CEA-CNRS, CE-Saclay, 91191 Gif-sur-Yvette, France
⁵ Institut Laüe-Langevin, Avenue des Martyrs, BP 156, 38042 Grenoble Cedex 9, France
⁶ Facultad de Ciencias, Universidad del Pais Vasco, Apdo 644, Bilbao, Spain

Corresponding author: ^a ronan.lefort@univ-lille1.fr

Received: 9 February 2001
Revised: 1 August 2001
Published online: 15 November 2001

Abstract

The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules. Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering results.