Rotational motions of CH4 molecules in weak orientational potentials of cubic symmetry

Nearly free rotational motions of CH4 molecules as substitutional impurities in argon, krypton, and xenon have been observed at low temperatures with inelastic neutron scattering. Besides energy transfer, the dependence of the scattered intensities on momentum transfer Q is used for the assignment o...

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Bibliographic Details
Published in:The Journal of chemical physics 1992-07, Vol.97 (2), p.1332-1342
Main Authors: ASMUSSEN, B, PRAGER, M, PRESS, W, BLANK, H, CARLILE, C. J
Format: Article
Language:English
Subjects:
Condensed matter: structure, mechanical and thermal properties
Exact sciences and technology
Lattice dynamics
Phonons and vibrations in crystal lattices
Physics
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Summary:Nearly free rotational motions of CH4 molecules as substitutional impurities in argon, krypton, and xenon have been observed at low temperatures with inelastic neutron scattering. Besides energy transfer, the dependence of the scattered intensities on momentum transfer Q is used for the assignment of the experimentally observed lines to the various transitions of a spherical quantumrotor in an orientational potential of cubic symmetry. The measured intensities are in good agreement with theoretical predictions based on the extended James–Keenan model. Measurements with high energy resolution on solid CH4 in its antiferrorotational phase II were devoted to the determination of the Q dependence of the tunneling lines and the nearly free rotor lines. The results give the first direct experimental evidence for the value 3 for the ratio of the orientationally ordered molecules to those which are orientationally disordered in CH4-II.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.463260