Effect of pressure and temperature on the O─H and O─D stretching, and translational vibrations in the Raman spectrum of ice clathrate

Abstract

Abstract Laser Raman spectra of H2O and D2O ice clathrate of type II structure containing tetrahydrofuran molecules as guests have been measured in the frequency ranges 100–350, 2800–3500 and 2200–2800 cm−1, temperature range 250–275 K and pressure range 1–1500 bar. The O─H stretching frequency decreases with increasing pressure and decreasing temperature. The frequency of the main peak in the translational vibration region increases with increasing pressure and decreasing temperature. The Gruneisen constant, -(δ In v/δ ln V) T , is 0·41 for O─H and −07·39 for O─D stretching, and 2·40 for translational vibrations, in both H2O and D2O clathrate. The increase in the O─H stretching frequency of the clathrate over hexagonal ice is about one-eighth, or less, of that expected on the basis of the increased average distance between the nearest-neighbour water molecules in it. This is attributed partly to the anharmonicity associated with the correlated motions of O─H stretching and O─H─O bending, and it is sugges...