Dielectrcc Behavior in the SrF₂-H₂O System. 2. Measurement at Low Temperatures

Dielectric properties of water adsorbed on the SrF₂ surface have been investigated under various conditions. A small relaxation was found at 33 kHz, 159 K, and a coverage of 0.74, besides a large relaxation observed at 298 K which had been described in part 1 of this series. This small relaxation is observed only when the physisorbed water molecules are present. Furthermore, the chord length of Cole-Cole plots for this relaxation is found to be a function of the coverage. These findings are interpreted in terms of the Debye-type rotational polarization of the adsorbed water and therefore confirm that the relaxation observed at 298 K is ascribed to the Maxwell-Wagner-type relaxation. An activation energy for the dipole rotation is also calculated from the variation of frequency corresponding to a maximum in the dielectric loss curve with temperature. This result suggests that the rotation of the water molecules condensed two-dimensionally is expected to be moee hindered than that of bulk liquid water, though not so much as in ice. The state of two-dimensionally condensed water on SrF₂ is discussed on the basis of the concept of lateral interaction.