The pressure dependence of the structure of deuterated ice VIII has been studied by time-of-flight neutron powder diffraction up to 10 GPa. The precision of the values of the intramolecular bond length O-D is ±0.003 Å or better at all pressures, and the rate of increase of the O-D bond length is found to be 0.0004(4) Å ${\mathrm{GPa}}^{\mathrm{-}1}$. This value is significantly smaller than previous estimates, which all incorporate the assumption that the form of the O-H potential is constant with pressure. It appears that this is not the case.

• Received 24 May 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.1192