Internal vibrational modes and hydrogen bonding in mixed crystals of HCN and DCN

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Abstract
Infrared spectra of the internal modes of mixed crystals of HCN and DCN have been studied as a function of composition. The variation of the normal mode frequencies as the composition changes cannot be explained by dipolar coupling alone, but long range coupling constants were required to enable a normal mode calculation to fit the observed spectra. The absolute absorption intensities of the internal modes were found to be independent of composition. The dramatic changes in the infrared intensities of the internal stretching modes which occur upon condensation are ascribed to a charge transfer mechanism which is characteristic for hydrogen-bonded systems.