The fluctuation hypothesis of hydrogen bonding

The infra-red and Raman spectra of normal and heavy water have been calculated, within the framework of the fluctuation hypothesis of hydrogen bonding, in good agreement with experiment. The necessary set of initial parameters estimated from the spectra of HOD and water vapour appears to be practically the same for H2O and D2O as well as for the spectra of infra-red absorption and both Raman polarizations. The frequencies and intensities of eigenvibrations for all types of spectra have been calculated using the method of partial oscillators, using 100 000 to 1 000 000 H2O (D2O) molecules variously perturbed by local environmental fluctuations. The calculation carried out is the first complete synthesis of spectral contours for water and gives their physical interpretation. It is shown that the main factor which determines the spectral shape for H2O and D2O together with its temperature variation is the intramolecular coupling of stretching vibrations of OH groups and the overtone of bending vibration (Fermi resonance). It is not necessary to postulate the existence of discrete species of aggregates nor the displacement of the equilibrium between them in the liquid. The band structure found reveals the inadequacy of the widespread method of interpretation of contour shapes by their computer decomposition into various components. (author)