Optical microscopy and Raman scattering of a single crystalline argon hydrate at high pressures

High-pressure raman study on single crystalline methane hydrate surrounded by methane in a diamond anvil cell

“…These phase behaviors were observed in two phase coexistent state between methane hydrate and water. In our high pressure Raman measurements of methane hydrate, no signal for the O-H stretching and lattice vibrations was observed in MH-III phase, in spite of the appearance of those signals in the same sO phase of Ar hydrate [12] and Kr hydrate [13]. This disappearance in MH-III phase is probably caused by the weak Raman signals of MH-III and the strong Raman spectra of the surrounding ice-VII.…”

Thermodynamic and Raman Spectroscopic Studies of Ar Hydrate System

“…(3)) also supports structural phase transition of Ar hydrate crystal. However, Shimizu, Hori, Kume, and Sasaki [10] have evaluated the multi occupancy of Ar atoms by the Raman spectra of Ar-Ar interatomic stretching vibration around 150 cm -1 . Manakov, Voronin, Kurnosov, Teplykh, Komarov, and Dyadin [14] have suggested the double occupancy of the structure-II Ar hydrate in the pressure region from (340 to 440) MPa based on neutron diffraction experiments at 293 K. Tanaka, Nakatsuka, and Koga [11] reported that double occupancy dominated over single occupancy above 270 MPa from van der Walls Platteuw theory.…”

“…Shimizu, Hori, Kume, and Sasaki [10] have reported that the Raman spectra of interatomic Ar-Ar interaction are detected around 150 cm -1 in the pressure range from (160 to 970) MPa at room temperature. They have claimed that this Raman spectrum corresponds to the multioccupancy of Ar atoms in the L-cage of structure-II.…”

High-pressure Raman study of methane hydrate "filled ice"

“…MH-sI and MH-II are well known to be a clathrate structure, whereas MH-III has a cage-less hydrogen-bonded water network, in which water molecules form channel structure and guest methane molecules are filled in their channels [5]. In the previous high pressure Raman measurements of methane hydrate, no signal for the O-H stretching and lattice vibrations was observed in the MH-III phase [6][7][8], in spite of the appearance of those signals in the same filled ice structure of Ar hydrate [9] and Kr hydrate [10]. In this paper, we measured the high-pressure Raman spectra for the O-H stretching vibration in the MH-III phase by growing MH-III crystals near the MH-II to MH-III phase transformation pressure of 1.9 GPa over several days, in order to clarify the origin of the appearance of O-H stretching vibration in the MH-III phase.…”