Effects in the Infrared Spectra of Crystals

Wojcik [91] developed a theory that is applicable to weak and medium-strength hydrogen bonds. The basic physical mechanism responsible for the energy and intensity distribution is the coupling between the high-frequency hydrogen-stretching 

The background of the theory of the observed IR-spectroscopic effect in crystals can be summarized in the following way. If in the harmonic approximation an isolated impurity molecule could be characterized by two adjacent levels (p and q), then in an anhannonic condition we get a new pair of more remote levels (/and g). As experiments show [80], in vibrational spectra the value of FR for isolated molecules is often comparable with the value of the DS for the molecular lattice (about several tens of cm ). Therefore, in zero approximation one can formulate expressions for the wave function of an excited impurity crystal. Using these expressions, Lisitsa and 

Yaremko [107] described that the separation between the/and g levels in an isolated molecnle is determined by the value of the FR interaction. The splitting of the non-degenerate/level (or g level) associated with different orientations of the molecules within the unit cell is determined by the valne of the intermolecnlar interaction. Both boundary cases of FR or DS effects conld be described. 

An overlapping of the wave fnnctions corresponding to/and g states is much smaller than that of the wave fnnctions corresponding to the Bethe components arising as a result of splitting of/and g states. Then,/and g levels resulting from p and q levels can be written separately because of the influence of anharmonicity. When exact resonance is present 

The ratio of intensities of bands with the same polarization will be 

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