High-Pressure Raman Study of Liquid and Crystalline CH₂F₂ up to 29, GPa

Abstract

High-pressure Raman spectra of liquid and crystalline CH₂F₂ were measured up to 29, GPa at 300, K in a gasketed diamond-anvil cell. Four solid phases have been found; the transition pressures of liquid-solid phase I, phase I-phase II, phase II-phase III and phase III-phase IV were determined to be 2.63, 3.82, 5.9 and 8.2, GPa, respectively. Among these, the solid phase I is an orientationally disordered (plastic) phase. The CH asymmetric stretching ν ₆ vibration (B₁) splits into the longitudinal optical (LO) mode and the transverse optical (TO) mode in the liquid and four solid phases. The wavenumbers of LO and TO modes and their wavenumber difference remarkably depend on the pressure, and drastically change at each phase transition point. The wavenumber of the CH stretching ν ₁ vibration (A₁) also shows a strong pressure dependence, and this behavior is compared with those of CHF₂Cl and CHF₃.