J. Phys. I France 3 (1993) 1617-1627
Phonons in orientationally disordered neopentane C(CD 3) 4M. Debeau1, Ph. Depondt1, B. Hennion2 and W. Reichardt3
1 Département de Recherches Physiques (UA CNRS 71), Université Pierre et Marie Curie, 75252 Paris Cedex 05, France
2 Laboratoire Léon Brillouin, CEN Saclay, 91191 Gif sur Yvette Cedex, France
3 Kernforschungzentrum, INFP, Postfach 3640, 7500 Karlsruhe, Germany
(Received 1 February 1993, accepted in final form 10 March 1993)
The phonons of deuteriated neopentane C(CD 3) 4 single crystals in the orientationally disordered phase were measured at T = 173 K by coherent inelastic neutron scattering, yielding very broad bands that spread, at a given energy, over a large portion of the Brillouin zone while sitting on an intense background. No librational mode was detected. Selection rule violations, presumably linked to disorder, were observed. The elastic constants are discussed in terms of rotational-translational coupling, and inelastic scattering results are compared with the molecular center of mass translational disorder as obtained from diffraction experiments providing a confirmation of a previous interpretation of these experiments.
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