Neutron scattering investigation of ice under hydrostatic helium pressure

Results of the inelastic incoherent neutron scattering investigations of wa ter and ice in the 273-114 K temperature interval under hydrostatic helium pressures up to 300 MPa are presented. It is shown that ice III is not form ed in the process of isobaric cooling, but at about 239 K, a helium clathra te crystallizes. Its inelastic incoherent neutron scattering spectrum is cl ose to that of ice II and this phase evidently is a solid solution of heliu m in ice II, in conformity with the results of a neutron diffraction study by D. Londono, et al. The position of the low-energy cutoff of the libratio nal band follows the regularity found earlier for the dependence of the gen eralized phonon density of states on density of high pressure phases of pur e ice.