Liquid Water−Acetonitrile Mixtures at 25 °C: The Hydrogen-Bonded Structure Studied through Infrared Absolute Integrated Absorption Intensities

The real and imaginary refractive index spectra of mixtures of water and acetonitrile over the full composition range at 25 °C were determined between 8000 and 700 cm-1 by calibrated multiple attenuated total reflection spectroscopy. Under the assumption of the Lorentz local field, the corresponding molar polarizability spectra, αm(ν) = α‘m(ν) + iα‘‘m(ν), were calculated and used to investigate the structure of the mixtures. The concentrations of water-bonded, acetonitrile-bonded, and non-hydrogen-bonded O−H groups, and of water-bonded and non-hydrogen-bonded acetonitrile molecules, were obtained from the integrated intensities COH and CCN, the areas under the O−H and C⋮N stretching bands in the να‘‘m spectra. The results indicate that no enhancement of the water structure (OH---O bonding) results from the addition of acetonitrile. In contrast, a monotonic decrease in the fraction of O−H groups that are bonded to oxygen is observed with increasing CH3CN content. At low acetonitrile concentration, xCH3...