X-ray diffraction study of liquid water in the temperature range 4–200°C

The scattering of X-rays from the free surface of liquid water in equilibrium with water vapour has been analyzed at 4, 25, 50, 75, 100, 150 and 200°C. Deuterium oxide at 4°C was also studied. The diffractometer used was specially designed for the study of liquid structure. The radial distribution functions derived from the experiments are in agreement with most of the previously published work on water showing, however, much higher resolution.Intensity and radial distribution functions have been computed for a model structure and compared to those derived from experiment. The model assumes an anisotropically expanded ice-I structure, surrounded by a continuous distribution of distances, as an adequate description of the short-range order in water. Occupancy of the large dodecahedral cavities typical for this structure was permitted. The model intensity and radial distribution functions are in quantitative agreement with those derived from experiment at all temperatures. Some thermodynamic properties estimated for the model structure are in essential agreement with those of liquid water.