Spectroscopic studies of vibrational relaxation and chemical exchange broadening in hydrogen-bonded systems. III. Equilibrium processes in the pyridine/water system

Raman (isotropic) scattering for the v 1 and v 12 modes of pyridine in binary solutions with water have been studied over the full concentration range. Band intensity data, based on a fit to three Lorentzian bands, are consistent, at least up to x W ≅ 0·6, with an equilibrium model which includes three different pyridine/water complexes Pyr2·W, Pyr·W and Pyr·W2, and which includes dimeric and trimeric water aggregates. The likely uniqueness of this interpretation is discussed in the light of recent mass spectrometric and infrared evidence that, especially at higher water concentrations, the binary mixture is more likely to contain, on the time scale of the experiment, a networked distribution of hydrogen-bonded interactions rather than a set of discrete ‘complexes’.