Characterization of the state of two-dimensionally condensed water on hydroxylated chromium(III) oxide surface through FT-IR, quasielastic neutron scattering, and dielectric relaxation measurements

The dynamic properties of water molecules adsorbed on the hydroxylated chro mium(III) oxide surface, whose two-dimensional critical temperature was 303 K, were investigated at around the two-dimensional critical temperature by FT-IR, quasielastic neutron scattering, and dielectric relaxation techniqu es. The Cr2O3 sample covered with monolayer water gives an IR band having a broad nature at similar to 3400 cm(-1), due to the mutual hydrogen bonding among the adsorbed water molecules. The quasielastic neutron scattering da ta have revealed that the motion of the adsorbed water molecules changes ac ross the two-dimensional critical temperature, ranging from the motion of t he supercritical fluid to that of a solidified phase with decreasing temper ature. The dielectric spectra observed at 298 K and at the coverage of 1.1 monolayers have been interpreted in terms of the presence of two relaxation s due to the interfacial and orientational polarizations. The characteristi c frequency of the relaxation for the latter polarization was estimated to be ca. 300 Hz. It is concluded from these findings that the two-dimensional ly condensed waters adopt the mutually hydrogen-bonded solid state having a commensurate structure with the hydroxylated (001) Cr2O3 surface below the two-dimensional critical temperature of this system. In addition, the inte rfacial polarization was explained in terms of a hopping model of protons o f the adsorbed molecules. The behavior of conductivity arising from this pr oton hopping also indicates the morphology of the two-dimensionally condens ed water below the monolayer coverage: the small clusters of water are form ed on the Cr2O3 surface.