Abstract
We have determined the full crystal structure of the high-pressure phase methane A. X-ray single-crystal diffraction data were used to determine the carbon-atom arrangement, and neutron powder diffraction data from a deuterated sample allowed the deuterium atoms to be located. It was then possible to refine all the hydrogen positions from the single-crystal x-ray data. The structure has 21 molecules in a rhombohedral unit cell, and is quite strongly distorted from the cubic close-packed structure of methane I, although some structural similarities remain. Full knowledge of this structure is important for modeling of methane at higher pressures, including in relation to the mineralogy of the outer solar system. We discuss interesting structural parallels with the carbon tetrahalides.
| Original language | English |
|---|---|
| Article number | 064504 |
| Journal | Journal of Chemical Physics |
| Volume | 133 |
| Issue number | 6 |
| DOIs | |
| State | Published - Aug 14 2010 |
Funding
We would like to thank A. Lennie and M. Hanfland for support and assistance in using, respectively, stations 9.5HPT (SRS) and ID09a (ESRF), L. F. Lundegaard for advice and help with the treatment and reduction of the x-ray data, and D. J. Francis for technical assistance with the neutron experiment on the HiPR/PEARL instrument (ISIS). The x-ray diffraction experiments at ESRF were performed as part of Long Term Project HS3090 on single-crystal diffraction at extreme conditions. This work was funded by the U.K. Engineering and Physical Science Research Council and supported by the U.K. Science and Technology Facilities Council through access to beamtime and other resources.