The infrared absorption bands due to the OD stretching vibrations of DP and HDO, and to the DP rotational vibrations, in the ordered forms of ice, ice II and ice IX, change little between 100 and lOoK. The frequencies and relative intensities of the zero-wave-vector OD stretching vibrations of these phases have been calculated in the harmonic and bond-moment approximations, and explain the main features of these bands. The features are less well resolved than is expected for an ordered molecular crystal, and this "hydrogen bonding effect" is attributed primarily to Fermi resonance between the fundamental states of the OD stretching vibrations and the isoenergetic continuum of high-order, overtone, and combination states of lower-frequency vibrations. The frequency of the OD stretching vibrations of HDO molecules isolated in H 2 0 ice Ih at lOOK is 2413.5 ± I em-I.

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. Can. J. Chem. 53,71 (1975).This paper presents the far-infrared spectrum and X-ray powder diffraction pattern of the structure I hydrate of cyclopropane at 100 OK, and the powder diffraction pattern of the isostructural ethylene oxide hydrate at 100 O K . Between 360and 100cm-I the absorption by cyclopropane hydrate is essentially identical to that by ethylene oxide hydrate, but is shifted to low frequency by about 2%. This shift is undoubtedly related to the hydrogen bonds being slightly longer in cyclopropane hydrate, whose cubic lattice parameter is 11.98 + 0.02 Acompared to 11.89 + 0.02 Aforethyleneoxide hydrate, bothat 110 + 20°K. Theabsorption by cyclopropane hydrate below 100 cm-' decreases rapidly with decreasing frequency; this confirms that the absorption plateau observed for ethylene oxide hydrate between l00and about 50cm-I is due to primarily rotational vibrations of ethylene oxide. A recent statement, that the orientational disorder of the water molecules need not be invoked to explain the far infrared spectrum of ice 1 h, is disputed.

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