Infrared Spectra of Molecules with Hydrogen Bonds

The unusual features of the infrared spectra of molecules with hydrogen bonds are discussed. It is shown that the broad hydrogen stretching bands associated with strong hydrogen bonds are not single bands, but groups of bands which are very sensitive to intermolecular influences. This is due to the anharmonicity of some parts of the (effective) molecular potential energy surface. This surface occasionally has two minima which implies typical double minimum phenomena. Variations in the intensity of the hydrogen stretching bands in going from the nonbonded to the bonded molecules is discussed and an explanation attributing this variation to the charge transfer associated with the hydrogen bond formation is offered.