Infrared Intensities of Liquids. 5. Optical and Dielectric Constants, Integrated Intensities, and Dipole Moment Derivatives of H₂O and D₂O at 22°C

We have recorded multiple attenuated total reflection spectra of liquid H2O and D2O, using the Spectra-Tech CIRCLE cell, and calculated from them the infrared optical and dielectric constants and molar conductivities from 9000 to 1250 cm-1 for H2O and from 8500 to 700 cm-1 for D2O. Our results agree well with the literature for H2O, while our results for D2O are the most extensive reported to date. We have calculated the dipole moment derivatives with respect to stretching and bending internal coordinates from the areas under the bands in our molar conductivity spectra. For lack of information, we have used the assumptions of the simple bond-moment model, a diagonal force field, and neglect of stretch-bend interaction. We found ∂μ/∂r for the stretching vibrations to be 3.02 D/Å ±1% and 3.04 D/Å ±0.5% for H2O and D2O, respectively, and ∂μ/∂θ for the bending vibration to be 0.73 D ±3% for H2O and 0.63 D ±5% for D2O. The two values for the stretching vibrations are indistinguishable, but this is not true for the bend. The disagreement for the bending vibration is probably due, at least in part, to our simulation of the absorption by three distinct bands of mixed Gauss-Lorentzian character, in order to try to separate the bending mode from the background absorption. It is probable that no such separation exists precisely. The bond moments for H2O and D2O agree with those calculated by the same approximations from literature data for HDO to about the extent allowed by the approximations. The intensities for liquid H2O are compared with those for water in the gas phase, in Ba(ClO3)2·H2O, in ice I, and in lithium β-aluminate. The intensity of the bending mode, v2(H2O), is essentially independent of the strength of the hydrogen bonds. That of the OH stretching modes increases with hydrogen bond strength in Ba(ClO3)2·H2O, liquid water, ice I, and lithium β-aluminate being 20, 17.5, 25, and 40, respectively, times more intense than in the gas. Explanations for this are briefly summarized. © 1989 American Chemical Society.