Liquid-like dynamical behaviour of water in silica gel at 5 K

Vibrational spectra of silica gel with low concentrations of water, 3 and 10%, were studied with inelastic neutron scattering (INS) at 5 K. The INS spectrum for the 3% water in silica gel shows dramatic changes compared to the spectra for other known ice phases in the energy transfer region of 2-150 meV. Its intermolecular librational band is shifted to lower energy by about 20 meV (or by a factor of 1.43) compared to ice-Ih, and has more in common with the librational band for water in the liquid state at 290 K. This indicates the softening of the corresponding transverse intermolecular force constants by a factor of 2 as compared to ice-Ih and could be understood by assuming that at low concentration, water in silica gel has a lot of weak and broken hydrogen bonds when compared to normal bulk ice.