Spectroscopy and dynamics of mixtures of water with acetone, acetonitrile, and methanol

Binary mixtures of water with acetone, acetonitrile, and methanol over their entire range of compositions have been studied spectroscopically and by using molecular dynamics (MD) simulations. We report absorption coefficients and indices of refraction over a frequency range from 3 to 55 ${\mathrm{cm}}^{\text{−1}},$ and from 400 to 1200 ${\mathrm{cm}}^{\text{−1}}.$ The far-infrared absorption of the mixtures is substantially less than that for ideal mixtures, and Debye time constants calculated from the spectra are longer for the real than for the ideal mixtures. Significant composition dependence is observed in the high frequency librational spectra of the mixtures, and is reproduced by the MD simulations. Single dipole and angular velocity spectra are also reported, as are detailed changes in the hydrogen bonding environment in the mixtures. There is a loss of tetrahedral water structure on mixing, yet water molecules have a strong tendency to aggregate, especially in the acetone and acetonitrile mixtures. Spatial distribution functions are reported for the acetone/water system.