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

Abstract

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 a low concentration, water in silica gel has a lot of weak and broken hydrogen bonds when compared to normal bulk ice.