Pressure effects on Raman scattering from solid HF and DF

Abstract

Single-crystal samples of HF and DF have been studied by Raman spectroscopy in a diamond-anvil cell up to pressures of about 12 GPa. Two translational, three librational, and two stretching modes were studied as a function of pressure. Comparison of the librational-mode frequencies in HF and DF using the expected isotope ratio has allowed the identification of one strong and two weak fundamental librational modes in HF and DF. This resolves some of the confusion in earlier studies on HF and DF. There is some evidence for a transition to a symmetric hydrogen-bonded phase in HF at about 6 GPa. There was no evidence for this transition in DF up to 12 GPa. An analysis of the pressure dependence of the symmetric-stretching modes in HF and DF has been done using the double-well model of Jansen et al. [Phys. Rev. B 35, 9830 (1987)] along with perturbation theory to give estimates of the pressure dependence of the barrier height.