STRONG-COUPLING MECHANISM FOR INTERPRETATION OF THE IR-SPECTRA OF THEHYDROGEN-BONDED IMIDAZOLE CRYSTAL

In this work we have attempted to provide a new interpretation of some complex spectral effects, recently observed in the high frequency reg ion of the IR spectra of hydrogen bonded imidazole crystals. The subje cts of our interest were effects corresponding to the intensity distri bution, the linear dichroism, the influence of temperature and the iso topic substitution of deuterium in imidazole molecules, measured in th e nu(N-H) and the nu(N-D) band ranges in the crystalline spectra. Base d on model calculations it was shown that the ''strong-coupling'' mode l was able to quantitatively reproduce the nu(N-H) and nu(N-D) band sh apes in the spectra of the imidazole crystal. This fact can be conside red as a basis for an explanation of the isotopic, polarization and te mperature effects in the spectra. The Fermi resonance effects have bee n found to be of a minor importance. The key property of the crystal r esponsible for the abnormal spectral properties of its H-bonds seems t o be the statistical disorder in the crystalline lattice, due to bendi ng of the H-bonds. This structural effect, along with the very specifi c selection rules in the IR for the centrosymmetric H-bonded dimers an d the correlation field interactions in the crystal, were considered t o be the main source of the spectral effects analyzed.