NEUTRON-SCATTERING STUDIES OF THE VIBRATIONAL-SPECTRUM OF HIGH-DENSITY AMORPHOUS ICE IN COMPARISON WITH ICE IH AND VI

The vibrational spectrum of recovered high-density amorphous (HDA) ice, obtained by pressurizing hexagonal ice Ih to 13 kbar at 77 K, has been studied by inelastic incoherent neutron scattering in the energy range from 1 to 120 meV at 80 K. The spectra of ice Ih and recovered high-pressure phase ice VI were also measured for comparison. In the translational band of the HDA ice spectrum, the first peak in the acoustic mode region is shifted by 2 meV towards high energies, but in the librational band the spectrum shows that the low-energy cut-off of this band shifts 13 meV towards low-energy transfers compared with ice Ih. Similarity of the main features of the spectra of HDA ice and ice VI have been observed and, thus, the dynamics of these ice phases should be determined by the same atomic correlations and force constants.