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
