Infrared Spectra of Ices II, III, and V in the Range 4000 to 350 cm—1

Abstract

The infrared spectra of Ices II, III, and V between 4000 and 350 cm—1 have been obtained. The ices were made at appropriate pressures and temperatures, cooled under pressure to liquid-nitrogen temperature, and removed from the pressure vessel. Mulls were made near liquid-nitrogen temperature using isopentane or perfluoropropane as mulling agents, and the spectra of the mulls at ∼100°K were recorded. The spectra of ices made from H2O, D2O, 5% H2O in D2O, 5% D2O in H2O, and, for Ices II and III, 1% D2O in H2O were obtained. In general features, the spectra of pure H2O and D2O Ices II, III, and V are similar to those of Ice I. For most bands there is a shift of frequency from that in Ice I towards the vapor frequencies, but the shift is small compared with the shift between Ice I and the vapor. Ices II, III, and V are therefore essentially fully hydrogen bonded and are probably four coordinated. This agrees with a proposed structure for Ice III. In Ices II and III the bands due to the O–H and the O—D stretching vibrations of HDO in dilute solution in D2O and H2O, respectively, show a good deal of fine structure, and are quite narrow, the half-width of the O—D bands being about 5 cm—1. These are by far the sharpest O–H (or O—D) stretching vibrations of hydrogen-bonded O–H———O groups so far observed. Clearly, breadth is not inherent in the O–H stretching bands of O–H———O. There is also a good deal of fine structure in the bands due to rotational vibrations of water molecules in Ices II and III, and much of this fine structure broadens and weakens when a small amount of H2O is added to D2O, and of D2O to H2O. The only simple explanation of this, and of the fine structure of the O–H stretching bands, is that the hydrogen atoms in Ices II and III are ordered. No corresponding fine structure occurs in Ice V, and the hydrogen atoms are probably disordered, as in Ice I.