In comparing the infrared spectra of liquid water and simple hydrates, two anomalies are noted which are apparently inexplicable in terms of presently acceptable theories of the liquid. These anomalies are explained in terms of a Maxwellian distribution of collisional interactions between water molecules, which when put in quantitative form reveals (1) that most molecules in the liquid are highly distorted by collisional perturbations, and (2) that there is a broad distribution of distortion among the molecules in the liquid. When translated into vibrational dynamics, these concepts lead to a continuum distribution of ν1 and ν3 modes of varying distorted molecules. It is shown that in its stretching motion, liquid water behaves dynamically as a continuum of OH bond oscillators of different frequencies, demonstrating both weak inter- and intramolecular vibrational interactions. A new interpretation of the infrared spectrum of liquid water is given in terms of this model, and other spectral evidence is offered in support of it.

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A study of the infrared spectra of varyingly deuterated thin films of gypsum has afforded information on the relative importance of intra- and intermolecular interactions in determining the stretching bands of water in the spectrum. This study has indicated that the internal forces in water are different for water in gypsum than they are for water in the vapor. It is further indicated that the water molecule in gypsum is much like the average molecule expected to exist in the liquid state.

The separation between uncoupled ν3 and ν1 frequencies of water symmetrically bound in both nonaqueous solvents and hydrates has been shown to vary linearly with the HOD stretching frequency of water, for both H2O and D2O. This relation, the FS correlation, has been explored theoretically and it has been shown to be useful for estimating geometry changes of water in hydrates, upon deuteration. It is also useful in determining the effect of cation coordination on the stretching frequencies of water molecules. A method is also developed, using this relation, for systematically analyzing the origin of the stretching bands of water in condensed systems.

A calculation is described for determining water molecule Frr force constants from observed HOD, H2O, and D2O vibrational frequencies. The calculations for water in the vapor and in the hydrates MnCl2·2H2O, FeCl2·2H2O, CoCl2·2H2O, and CuCl2·2H2O indicate a large increase in Frr with hydrogen bonding. Various contributions to Frr are considered, and its increase is attributed to an enhancement of the effective charge on water hydrogens with increased hydrogen bonding.

Room- and low-temperature infrared spectra of copper chloride dihydrate and its deutero modifications have been obtained, as well as polarized spectra of oriented polycrystalline films of the hydrate. Bands due to vibrations of H2O, D2O and HOD molecules in the hydrate, as well as their polarization, are considered in terms of the crystal structure and previous interpretations of the vibrational bands of the solid.

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Polarized and unpolarized infrared spectra have been obtained for copper chloride dihydrate samples, containing low mole ratios of H2O and D2O. The positions of the absorption bands of these samples are shown to differ from those of samples, containing high percentages of these same molecules. The spectral differences noted are shown to be related to the interactions between water molecules in the solid. Furthermore, a criterion is provided for sensing a variation of hydrogen bond strength with deuteration, and the origin of bands in the ν2 overtone regions of H2O, D2O, and HOD is also considered.