徳島大学 教育・研究者情報データベース(EDB)

1. 吉田 健([徳島大学.大学院社会産業理工学研究部.理工学域.応用化学系.物質機能化学分野]/[徳島大学.理工学部.理工学科.応用化学システムコース.物質機能化学講座])

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2. (英) Suhara Shinnosuke / (日) 須原 慎之助 / (読) すはら しんのすけ

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3. 野口 直樹([徳島大学.大学院社会産業理工学研究部.理工学域.応用化学系.物質機能化学分野]/[徳島大学.理工学部.理工学科.応用化学システムコース.物質機能化学講座])

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(英) Effect of Cage Occupancies on Molecular Vibrations of Methane in Structure H Clathrate Hydrate: Ab Initio Molecular Dynamics Simulation

(英) The structure H (sH) of methane hydrate, which has a distinctive structure with large (LL) cages capable of encapsulating multiple methane molecules, has been suggested as a methane reservoir in large icy bodies such as Titan, making it important in planetary science. This high-pressure phase, which exists in the GPa range, lends itself to the study of methane states and dynamics using powerful experimental techniques such as IR and Raman spectroscopy. However, the interpretation of the vibrational spectra of methane in the sH structure has been challenging because of the spectral complexities. The signals attributed to the methane molecules in the LL cage, as well as those of the other two cage types, overlap in the spectra. In this study, we investigated the microscopic origins of the shape of the C-H stretching vibration spectrum of methane in the LL cage using ab initio molecular dynamics (AIMD) simulations. For a single methane molecule in the LL cage, the ν band of the C-H stretching mode was observed at a higher frequency typical of isolated molecules in vacuum due to the large size of the LL cage. As the number of methane molecules in the LL cage increased beyond one, a tendency to blue-shift with increasing methane occupancy was observed, consistent with a loose-cage-tight-cage model. By characterizing the time correlation function of methane stretching vibrations based on the solvation number of methane and water molecules proximal to methane within the LL cage, we showed that the complicated spectral line shape observed in cases of higher methane occupancy in the LL cage resulted from the wider variation of the solvation shell states. Analysis of the solvation structures of the AIMD trajectories provided interpretations of the experimental spectral line shape, demonstrating the complementary nature of AIMD to the experiment and its effectiveness in analysis.

1. (英) Article.ELocationID: 10.1021/acs.jpcb.4c01790

2. (英) Article.PublicationTypeList.PublicationType: Journal Article