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Science 27 September 2002:
Vol. 297. no. 5590, pp. 2247 - 2249
DOI: 10.1126/science.1075394

Reports

Hydrogen Clusters in Clathrate Hydrate

Wendy L. Mao,12* Ho-kwang Mao,2 Alexander F. Goncharov,2 Viktor V. Struzhkin,2 Quanzhong Guo,2 Jingzhu Hu,2 Jinfu Shu,2 Russell J. Hemley,2 Maddury Somayazulu,3 Yusheng Zhao4

High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.

1 Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
2 Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
3 High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
4 Los Alamos Neutron Science Center (LANSCE), Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
*   To whom correspondence should be addressed. E-mail: wmao{at}uchicago.edu


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