Europhys. Lett.
Volume 48, Number 3, November 1999
Page(s) 269 - 275
Section Atomic and molecular physics
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00476-x

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

1 InstitutfürExperimentelleundAngewandtePhysikderUniversitätKiel-Kiel,Germany
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)

PACS. 31.70${\rm -f}$ - Effects of atomic and molecular interactions on electronic structure.
PACS. 36.20${\rm -r}$ - Macromolecules and polymer molecules.
PACS. 33.20${\rm -t}$ - 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 $\rm CH_4$ 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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