Methane hydrate has a unique structure that the host water framework forms two kinds of cages,
which contain one methane molecule each. Therefore, it has been expected that there may exist
three kinds of translational modes of a methane molecule and also the distortion of translational
mode of host water molecules compared with normal ice. We need information of the host and
guest molecular dynamics over the wide momentum and energy transfer region for studying such
dynamics. In this study inelastic neutron measurements were carried under 40 K with MARI
spectrometer at ISIS in UK, TAS at JRR-3 and CAT at KENS in Japan. For the methane
molecular motion we could confirm its freelike rotation by complementary use of MARI and
TAS spectra. After the subtraction of the scattering intensity of the rotation evaluated by the free
rotation model from the experimental data, three kinds of translation modes were identified at
first experimentally. On the experimental spectra there still remains the excess intensity which
could not explain the single mode excitation. The libration mode of the water framework shows
the different momentum and energy transfer dependence with those of normal ice. The feature of
the libration mode is resemble to ice-IX, that could be considered as a proton ordering of the cage
structure appeared in ice-II, VIII and IX.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1293 |
| Date | 07 1900 |
| Creators | Kamiyama, T., Seki, N., Iwasa, H., Uchida, T., Kiyanagi, Y., Ebinuma, Takao, Narita, Hideo, Igawa, N., Ishii, Y., Bennington, S.M. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Rights | Kamiyama, Takashi |
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