FOURIER-TRANSFORM INFRARED-SPECTROSCOPY OF H2O MOLECULES ON THE CR2O3 SURFACE

Physical adsorption and two-dimensional phase change of H2O molecules on a hydroxylated Cr2O3 surface were studied by Fourier-transform infrared (IR) spectroscopy. Two kinds of adsorption were confirmed spectroscopically: (1) adsorption of H2O molecules on localized OH groups and (2) adsorption of H2O molecules on special OHs, leading to two-dimensional condensation at the critical temperature for which chemical shifts of the two stretching modes of OH vibration were observed. A two-dimensional phase change of physisorbed H2O molecules was demonstrated by the fact that due to physisorbed H2O molecules interacting through hydrogen bonds broad bands were sharpened at the two-dimensional critical temperature as well as due to OHs working as adsorption sites. There are large proportions of OHs on the Cr2O3 surface other than the above two types, which were found inactive for H2O adsorption.