High-pressure elastic properties of the orientationally disordered and hydrogen-bonded phase of solid HCl

By using in situ Brillouin spectroscopy in a diamond-anvil cell, we have measured the direction-dependent acoustic velocities and the refractive index in the orientationally disordered and hydrogen-bonded solid phase I of hydrogen chloride (HCl) at pressures up to 4.5 GPa and 300 K, leading to the first determinations of adiabatic elastic constants (C-11, C-12, and C-44), bulk modulus (B-S), and the elastic anisotropy (A) to 4.5 GPa. These results are compared with those of solids of the same type H2S and NH3. We investigate the effect of the strength of hydrogen bonds on the A value which is sensitive to the rotation-translation coupling of molecular motions under compression. [S0163-1829(99)01318-1].