An X-ray study of the effect of pressure on the structure of liquid water

Abstract

The molecular pair correlation functions of liquid H2O have been obtained in the pressure range 1–2000 bar. A strong structural inhomogeneity of liquid water resulting from fluctuations of the entropy and density has been found. This gives rise to a complicated shape of the distribution of the intermolecular distances in the first coordination sphere. The coordination number is equal to approximately 4·4, but not more than 2·5 of the total number of the nearest molecules can form a tetrahedral short-range order. It has been established that the effects of both pressure and temperature on the water structure are fairly alike; they lead to a decrease of tetrahedral ordering. The rate of decrease of the separation between the nearest molecules is found to be approximately 0·03 Å kbar-1; this is much larger than is usually supposed. The results have been interpreted in terms of a percolation model.