Title: Raman spectroscopic observations of methane-hydrate formation and hydrophobic hydration around methane molecules in solution
Abstract:To reveal the hydrophobic hydration process of methane molecules dissolved in water, Raman spectra of dissolved methane (CH 4 ) in water were measured under various conditions. The conditions include ...To reveal the hydrophobic hydration process of methane molecules dissolved in water, Raman spectra of dissolved methane (CH 4 ) in water were measured under various conditions. The conditions include water saturated with CH 4 gas, waterCH 4 solution with CH 4 hydrate crystals in equilibrium, and also during hydrate decomposition. The symmetric CH stretching mode of the CH 4 molecule in water is a single peak at 2910 cm 1 with a half-width of approximately 5 cm 1 . These results indicate that the size of the space for the CH 4 molecules, called the hydration shell, is between the large and small cages of the hydrate crystal, but it has a broad size distribution. To better understand the CH 4 -molecule vibrations, its spectrum in water was compared with its spectra in liquid carbon dioxide (CO 2 ) and in liquid ethane (C 2 H 6 ). These spectra were very similar to those observed in water, except that the peak widths were sharper than those in water. This suggests that the broadening of the shell-size distribution is due to the way the CH 4 molecules affect the hydration shell. On the other hand, when the system included hydrate crystals, a double CH 4 peak arose due to structure in the aqueous solution near the crystal surface. This indicates that a cage-like structure can exist in the water phase. Compared with the decomposition experiment, the cage-like structure is likely due to the presence of the bulk hydrate crystal and is different from the hydration shell for the dissolved CH 4 molecules. PACS Nos.: 81.10Dn, 33.20FbRead More
Publication Year: 2003
Publication Date: 2003-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 16
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