Thermodynamic stability of hydrogen clathrates
Authors:
- 9 December 2003
- journal article
- Published by National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 100 (25) , 14645-14650
Abstract
The stability of the recently characterized type II hydrogen clathrate [Mao, W. L., Mao, H.-K., Goncharov, A. F., Struzhkin, V. V., Guo, Q.,et al. (2002)Science297, 2247–2249] with respect to hydrogen occupancy is examined with a statistical mechanical model in conjunction with first-principles quantum chemistry calculations. It is found that the stability of the clathrate is mainly caused by dispersive interactions between H2molecules and the water forming the cage walls. Theoretical analysis shows that both individual hydrogen molecules andnH2guest clusters undergo essentially free rotations inside the clathrate cages. Calculations at the experimental conditions – 2,000 bar (1 bar = 100 kPa) and 250 K confirm multiple occupancy of the clathrate cages with average occupations of 2.00 and 3.96 H2molecules perD-512(small) andH-51264(large) cage, respectively. The H2–H2O interactions also are responsible for the experimentally observed softening of the H—H stretching modes. The clathrate is found to be thermodynamically stable at 25 bar and 150 K.Keywords
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