Structure and dynamics of nonaqueous mixtures of dipolar liquids. I. Infrared and far-infrared spectroscopy

Abstract

Mixtures of acetone/methanol, acetonitrile/methanol, and acetone/acetonitrile over their whole composition range were studied with infrared and far-infrared (THz) spectroscopy. Experimental spectra of all mixtures were obtained below 120 cm−1, and spectra of methanolic mixtures were also measured from 400 to 1000 cm−1. The mixtures display ideal absorption spectra below 120 cm−1, contrasting with significant nonidealities in the absorption of aqueous mixtures in the same frequency range. Dramatic changes as a function of composition were found in methanolic mixtures at higher frequencies. The high frequency librational band of methanol, centered at 670 cm−1, shifts to substantially lower frequencies upon dilution, indicating marked changes in the librational motion of the hydroxyl hydrogen of methanol. This band is a sensitive probe of the hydrogen bonding environment experienced by methanol molecules.