RAMAN-SPECTROSCOPIC STUDY OF SOLVATION STRUCTURE IN ACETONITRILE WATER MIXTURES

Raman spectroscopy is used to probe the CN stretching frequency of acetonitrile as a function of concentration in water. The CN band is modeled as the sum of two Gaussians. The concentration dependence of area and width for each of the Gaussian components provides experimental support of an equilibrium between two forms of acetonitrile in solution. In addition, the concentration dependence of each of the bands correlates well with the thermodynamically related Kirkwood-Buff integrals (G(ij)). Specifically, both the vibrational bandwidth and G(ii) exhibit maxima near X(CH3CN) almost-equal-to 0.3, suggestive of strong interaction between acetonitrile molecules. The frequency shift of the CN band exhibits a linear dependence on the dielectric constant of protic solvents.