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Phase Transitions in Solid Methane Up to 60 Kbar

Published online by Cambridge University Press:  21 February 2011

N.J. Trappeniers
N.J. Trappeniers*
Affiliation:
Van der Waals Laboratory, University of Amsterdam, The Netherlands (290th publication of the Van der Waals Fund)
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Extract

Solid methane has been a favourite subject for the study of phase transitions ever since the discovery by Clusius [1] of the phase transition α → β at 20.4 K in CH4. The reasons for the sustained interest in solid CH4 may be attributed to the following facts. i. The CH4 molecule has an almost spherical shape with a slight TD anisotropy. As a result, CH4 crystallizes below 90.7 K into a plastic crystal, α, of cubic symmetry, exhibiting almost complete rotational freedom of the molecules. ii. The CH4 molecule is very small in size with a low moment of inertia (I × 1040 g cm2 = 5.34 in CH4 and 10.64 in CD4), leading to a large rotational kinetic energy and related quantum effects at low temperature. iii. The protons in CH4 and the deuterons in CD4 carry a nuclear spin resp. Ip = 1/2 and I. = 1, which gives rise to spin-isomerism. Thus, CH4 has three spin varieties, meta (A1, In = 2), ortho (T2, in = 1) and para (E, In = 0). The isomerism may be expected to have profound influence on the phase diagram of solid methane.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 22: Symposium NY – High Pressure in Science and Technology , 1983 , 173
Copyright
Copyright © Materials Research Society 1984

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References

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