Infrared spectroscopic study of water-aromatic hydrocarbon mixtures at high temperatures and pressures.

This paper reviews recent infrared studies on water-aromatic hydrocarbon mixtures. It mainly deals with infrared absorption of HDO in hydrocarbons measured as a function of temperature and pressure in the 373-648 K and 100-350 bar ranges, respectively, The intensity ratio of a hydrogen-bonded OH band to a hydrogen-bond-free OH band increases with increasing temperature. This fact indicates that the rate of increase in water solubility in the hydrocarbons is large enough to surmount the entropy effect which is unfavorable to water-water association. A good correlation between the peak frequency of the hydrogen-bond-free band and ionization potential of solvent hydrocarbons suggests that the concept of pi -hydrogen bonding between water and aromatic hydrocarbons is useful even at high temperatures and pressures. At higher temperatures, the two OH bands mentioned above merge into a single band, which suggests that a water molecule rotates rather freely even in a hydrogen-bonded water cluster at high enough temperature. Water concentration and density of a hydrocarbon-rich phase are estimated from infrared intensities. Both of them show remarkable pressure dependence near an extended line of the three-phase coexistence curve in the phase diagram. This behavior should be characteristics of fluid mixtures near the critical region.