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- C. Gutt
- Institut für Experimentelle und Angewandte Physik der Universität Kiel, Kiel, Germany
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- B. Asmussen
- Institut für Experimentelle und Angewandte Physik der Universität Kiel, Kiel, Germany
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- W. Press
- Institut für Experimentelle und Angewandte Physik der Universität Kiel, Kiel, Germany
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- M. R. Johnson
- Institute Laue-Langevin, Grenoble, France
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- Y. P. Handa
- National Research Council of Canada, Ottawa, Ontario, Canada
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- J. S. Tse
- National Research Council of Canada, Ottawa, Ontario, Canada
抄録
<jats:p>We present the results of a high-resolution neutron diffraction experiment with a fully deuterated methane hydrate type I at temperatures of 2, 100, and 150 K. Precise crystallographic parameters of the ice-like D2O lattice and the thermal parameters of the encaged methane molecules have been obtained. The parameters of the host lattice differ only slightly from values found for hydrates with asymmetric guests included, which leads to the conclusion that the host lattice of structure I is only a little adaptive. At low temperatures (2 K) the methane molecules in both types of cages present in structure I occupy positions in the center of the cages. At higher temperatures the thermal parameters in both types of cages reflect the surrounding cage geometries or more precisely the translational potentials of the cages. The orientational scattering length density of the CD4 molecules has been analyzed in terms of a multipole expansion with symmetry adapted functions [Press and Hüller, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. A29, 252 (1972); Press, ibid. A29, 257 (1972)]. In both types of cages we found only small modulations of a spherically symmetric scattering density accounting for almost free rotations of the methane molecules. The large and asymmetric cage leads to a somewhat more pronounced modulation of the orientational density than in the small dodecahedral cage. The orientational probability distribution function (PDF) remains nearly unchanged from 2 to 150 K. At 200 K we observed the time-resolved decomposition of the hydrate structure I into hexagonal ice Ih.</jats:p>
収録刊行物
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- The Journal of Chemical Physics
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The Journal of Chemical Physics 113 (11), 4713-4721, 2000-09-15
AIP Publishing
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詳細情報 詳細情報について
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- CRID
- 1361981468497419520
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- NII論文ID
- 30015629125
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- ISSN
- 10897690
- 00219606
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