Effect of temperature and pressure on translational lattice vibrations and permittivity of ice

Abstract

Laser-Raman spectra of hexagonal H2O and D2O ice have been measured in the frequency range 100–350 cm−1, temperature range 25–272 K, and pressure range 1–1600 bar. The frequency of the main peak due to translational lattice vibrations νT, which appears near 220 cm−1, decreases with increasing temperature at an increasing rate. νT increases linearly with applied pressure. An analysis of the variation of νT with temperature and pressure shows that ∼55% increase in νT on cooling is due to the intrinsic dependence of translational vibrations on temperature and ∼45% due to the accompanied decrease in the distance between the nearest oxygen atoms in ice. For the same amount of decrease in the distance, isobaric cooling increases νT twice as much as isothermal compression near 255 K. The Grüneisen constant −(∂ ln νT/∂ ln V) is 1.84 at 255 K. The contribution to the refractive index and permittivity from translational vibrations has been calculated over a wide range of temperature. The decrease in the limiting high frequency dielectric permittivity of ice with decreasing temperature or increasing pressure is qualitatively consistent with the observed change in the main frequency of lattice vibrations.