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

This paper reviews recent infrared studies on water-aromatic hydrocarbon mi xtures. It mainly deals with infrared absorption of HDO in hydrocarbons mea sured as a function of temperature and pressure in the 373-648 K and 100-35 0 bar ranges, respectively, The intensity ratio of a hydrogen-bonded OH ban d to a hydrogen-bond-free OH band increases with increasing temperature. Th is fact indicates that the rate of increase in water solubility in the hydr ocarbons is large enough to surmount the entropy effect which is unfavorabl e to water-water association. A good correlation between the peak frequency of the hydrogen-bond-free band and ionization potential of solvent hydroca rbons suggests that the concept of pi -hydrogen bonding between water and a romatic hydrocarbons is useful even at high temperatures and pressures. At higher temperatures, the two OH bands mentioned above merge into a single b and, which suggests that a water molecule rotates rather freely even in a h ydrogen-bonded water cluster at high enough temperature. Water concentratio n and density of a hydrocarbon-rich phase are estimated from infrared inten sities. Both of them show remarkable pressure dependence near an extended l ine of the three-phase coexistence curve in the phase diagram. This behavio r should be characteristics of fluid mixtures near the critical region.