Raman spectroscopic studies of the OH stretching region of low density amorphous solid water and of polycrystalline ice Ih

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Abstract
Extensive experimental studies of the OH stretching region of the Raman spectra of polycrystalline ice Ih and low density amorphous solid water (H2O (as)) are reported. Analysis of these spectra, using insights from theoretical calculations, leads to the following conclusions: (i) The overall span and distribution of features in the spectra result from strong intermolecular coupling of OH oscillators. This coupling is so strong that the solids cannot be considered to be composed of weakly perturbed water molecules, and the identification of features of their spectra with molecular vibrations is not useful. (ii) At the low end of the OH stretching region there is a totally symmetric mode—that is the amplitudes of motion on all oscillators are in phase, but these amplitudes vary erratically from site to site in the solid. The temperature dependence of the shift in frequency of this mode is likely all accounted for by thermal expansion, the temperature dependence of its FWHM is accurately described as due to scattering by optical phonons with effective frequency 200 cm−1. (iii) The earlier proposed interpretation of the Raman spectrum of H2O(as) by Venkatesh, Bates and Rice [J. Chem. Phys. 63, 1065 (1975)] is withdrawn. Their interpetation was based on the assumptions that they had observed the spectrum of high density H2O (as), which we now believe to be incorrect, and that the solid could be considered an assembly of weakly perturbed water molecules, which we now believe to be untenable.