Effect of temperature and large guest molecules on the C-H symmetric stretching vibrational frequencies of methane in structure H and I clathrate hydrates.

ABSTRACT: Large molecules such as 2-methylbutane (C₅H₁₂) or 2,2-dimethylbutane (C₆H₁₄) form structure H (sH) hydrates with methane (CH₄) as a help gas. In this study, the Raman spectra of the C-H symmetric stretch region of CH₄ enclathrated within various sH hydrates and structure I CH₄ hydrates were analyzed in the temperature range 137.7-205.4 K. Thermal expansions of these sH hydrate samples were also measured using powder X-ray diffraction. Symmetric stretch vibrational frequencies of CH₄ in host-water cages increased because of varying temperature, and the sizes of the host-water cages also increased; variation of CH₄ in small cages was less than in larger cages. Comparing the variations of the C-H symmetric stretching frequencies of CH₄ in gas hydrates with varying pressure and temperature, we suggest that the observed trend is caused by thermal vibrations of the CH₄ molecule in water cages.

SUBMITTER: Fuseya G 

PROVIDER: S-EPMC9053386 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature