INFRARED SPECTRUM AND STRUCTURE OF LIQUID WATER

Abstract

The infrared spectrum of HDO at low concentrations in H 2 O and in D 2 O was studied between 0° and 130° by a double-beam technique. Each of the three fundamentals of HDO shows nearly Gaussian contours, complete absence of shoulders, and a single maximum at a frequency intermediate between those of HDO in ice and in vapor. Increase of temperature causes a gradual shift of each band in the direction of the frequency in vapor. These observations fully support the "continuum" models of the structure of liquid water and present strong evidence against the "mixture" models. It is concluded that hydrogen bonds in liquid water have a broad, smooth, single-peaked distribution of strengths which gradually shifts with temperature. The hydrogen bonds at one end of this distribution have strengths comparable to those in ice, whereas those at the other end are very weak. These extremes do not correspond to distinct molecular species. Every description of liquid water in terms of "broken" and "unbroken" bonds, or "monomers" and "clusters", is therefore arbitrary.