High-pressure crystallography of methane: a low-temperature neutron diffraction study in the 1–5 GPa range

Abstract

We report the preliminary results of our recent low-temperature, high-pressure neutron diffraction study of deuterated methane. Contrary to earlier spectroscopic studies of hydrogenous methane, we find no evidence of any structural change between 1 and 5 GPa at 25 K and show that the diffraction patterns can be indexed and refined with the room temperature high-pressure structure of phase A. Our results suggest that either methane shows a remarkably strong isotopic effect or the spectroscopic changes observed are not indicative of structural phase transitions.

Keywords:

• high-pressure
• methane
• structure

Acknowledgements

We thank Gerard Hamel, Jean-Luc Laborier and Claude Payre for their invaluable technical assistance during the experiment, and Richard Nelmes for assistance in writing this report. We acknowledge support from the UK Engineering and Physical Sciences Research Council.