Europhys. Lett, 48 (3), pp. 269-275 (1999)
Quantum rotations in natural methane-clathrates from the Pacific sea-floor
C. Gutt 1, B. Asmussen 1, W. Press 1, C. Merkl 1,
H. Casalta 2,
J. Greinert 3
G. Bohrmann 3, J. S. Tse 4 and A. Hüller 5
2 Institute Laue-Langevin - Grenoble, France
3 GEOMAR, Universität Kiel - Kiel, Germany
4 National Research Council of Canada - Ottawa, Ontario, Canada
5 Institut für Theoretische Physik I, Universität Erlangen-Nürnberg, Germany
(received 15 April 1999; accepted in final form 2 September 1999)
- Effects of atomic and molecular interactions on electronic structure.
PACS. 36.20 - Macromolecules and polymer molecules.
PACS. 33.20 - Molecular spectra.
We report inelastic neutron scattering experiments from natural methane hydrates sampled from the Pacific sea-floor during an expedition of the research ship SONNE. The experiments verify directly the content of methane by measuring the rotational spectrum of the molecules. The existence of almost free rotational levels excludes off-center positions of the molecules in the cages. In addition we could assign the observed peaks in the energy regime up to 5 meV to rotational excitations only. The observed relative sharp excitations prove a surprisingly good crystallinity of the geological sample. The finite width is attributed to frozen-in hydrogen disorder of the ice cages.
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