VIBRATIONAL-SPECTRA AND POINT-DEFECT ACTIVITIES OF ICY SOLIDS AND GAS-PHASE CLUSTERS

This review focuses on the vibrational spectra of icy solids, in particular ice I, and the value of the spectra in monitoring point defect activity within the various hydrogen-bonded networks. After a brief review of the spectra of icy substances containing only H20 or D20, an attempt is made to update both the spectroscopic data and the interpretation by emphasizing recent results for isotopically diluted/decoupled D20 in H20 ice I, amorphous ice and the clathrate hydrates. These data are informative of the magnitude of the intramolecular and intermolecular O-H oscillator coupling strengths, the strength of the Fermi interaction between and 2v2, the influence of symmetric hydrogen bonding on the directionality of the water-molecule bond-dipole-moment derivative, and, perhaps most importantly, the spatial extent of the collective vibrations in icy substances. The interpretation of the spectra retains, and expands, the assignment of Whalley (1977) based on the view that intermolecular coupling forces, caused by hydrogen bonding (V3) and the polarization field (v3), give rise to collective oscillations that dominate the appearance of the infrared and Raman stretching-mode band complexes. The classical conductivity data for icy substances is generally understood in terms of the combined activity of ionic and orientational point defects. The incorporation of a water isotopomer (e.g. D20) in the icy network of a second (H20) is possible because such point defect activity, required for isotopic exchange, is lacking at very low temperatures. The simplicity and uniqueness of the spectra of the isotopically decoupled units allows monitoring of the [D20], [HOD] and [(HOD)2]. Consequently, after an isotopomer is incorporated within an icy substance, isotopic exchange, stimulated by one of several approaches, may be monitored. A review of the data for the point defect activities for several icy substances suggests that the theory developed by Jaccard (1959) and others from classical conductivity data is basically correct. However, a modification appears to be necessary to account explicitly for an activation energy for the proton hopping which results from intrinsic shallow trapping of the protons. A limited review of the concept, that crystallization rates of icy substances are dependent on the activity of L-defects, identifies a need for additional study. © 1990 Taylor and Francis Group, LLC.