Motions of Water Molecules in Potassium Ferrocyanide Trihydrate, Water, and Ice: A Neutron Scattering Study

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Abstract
The motions of H2O molecules in ferroelectric potassium ferrocyanide trihydrate, water, and ice have been investigated by total cross section and differential inelastic scattering measurements with cold neutrons. The results show no significant change in the average rotational or translational freedom of the water molecules in KFCT at or near its ferroelectric transition. The inelastic neutron spectra for KFCT exhibit broad peaks at about 425 and 160 cm−1, both above and below the transition, which are assigned primarily to the librational and optic translational modes of the H2O molecules, respectively. Moreover, both the total cross section and inelastic scattering results indicate a greater freedom of motion of the H2O molecules in the KFCT lattice than in either water or ice. In addition, a decrease in the total cross section of H2O, and in its variation with neutron wavelength is observed at the water—ice transition, indicating a significant change in the frequency distribution. The neutron results are compared with the results of NMR and infrared measurements.