A simple molecular orbital treatment is presented to explain the bonding in trihalide ions, X3−, XY2−, and XYZ−, and bifluoride ion, HF2−. The M.O.'s are formed from linear combinations of npσ halogen orbitals, and the 1s hydrogen orbital and stable bonding M.O.'s are obtained without the introduction of higher atomic orbitals. Applications are suggested in prediction of other stable species and low energy reaction intermediates.

The stretching and bending vibrational modes of the hydrogen bonded polymers of water have been studied by the matrix isolation technique using solid nitrogen at 20°K as a matrix. Absorptions are assigned to water monomers (3725, 3627, and 1600 cm—1), to dimers (3691, 3546, and 1620 cm—1) and to higher polymers (3510, 3355, 3318, 3222, and 1633 cm—1). The frequencies suggest that the dimers have cyclic rather than open (or bifurcated) structures. The absorption coefficients of the bending modes decrease slightly in the higher polymers while those of the stretching mode increase by a factor of about twelve. This intensity behavior cannot be explained solely on the basis of enhanced ionic character of the O–H group in the hydrogen bond.

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Empirical correlations between X–H≡Y distance R and frequency shift of the X–H stretching motion Δv are presented for O–H≡O, N–H≡O, and N–H≡N hydrogen bonds. A linear correlation is possible provided a distinct straight line is assumed for each hydrogen bond type. The equations of the best straight lines and standard deviations are: O−H···O  Δν(cm−1)=4.43·103(2.84−R) σ(Δν)=199cm−1N−H···O  Δν(cm−1)=0.548·103(3.21−R)σ(Δν)=24cm−1N−H···N  Δν(cm−1)=1.05·103(3.38−R)      ?

Three spectral properties, frequency shift Av, band width v>/, and integrated intensity B, have been measured for a variety of hydrogen bonding systems X-H • • Y in solution. A linear relation is found between Av and yy, which is applicable to a wide variety of systems: yy, = 0.72 Ay + 2.5 cm.-1. A simple monotonic relation is also found between Ay and B. The intensity is discussed with reference to the intensities of X-H bending modes; polarization in the base molecule is suggested.