Infrared spectroscopy of liquid water-N,N-dimethylformamide mixtures

The real and imaginary molar polarisability spectra (α′m(ν̃) and α″m(ν̃), respectively) of mixtures of water and N,N-dimethylformamide (DMF) over the full composition range (0 ≤ xDMF ≤ 1) at 25 °C were determined between 4000 and 700 cm− 1 by using a calibrated single reflection attenuated total reflection (ATR) technique. The composition dependent mole fractions of OH groups hydrogen bonded to water or DMF, together with the fractions of carbonyl groups hydrogen bonded to water or free were obtained from the integral intensities COH, and CCO of the ν(OH) and ν(CO) bands, respectively. As for the acetonitrile-water system (studied by other groups), a continuous composition dependence of the mole fraction of OH oscillators in different bonding situations was found with practically the same segmentation of the full composition range (xI = 0.2-0.3, xII = 0.7-0.8). From these observations, the existence of relatively large, stable water or DMF aggregates is proposed for xDMF between xI and xII with hydrogen bonding between water and DMF occuring only at the interfaces between the aggregates.