X-ray scattering in liquid water at pressures of up to 7.7 kbar: Test of a fluctuation model

TLDR

Pair correlation functions of liquid water at 20 °C under pressures up to 7.7 kbar were measured and analyzed. The authors propose using water as a model system to probe fundamental aspects of the liquid state. They interpreted the data through nearest‑environment fluctuations and fitted the g(r) curves with a SIMPLEX‑derived sum of correlation functions from heavily distorted solid‑phase structures. The study shows that pressure up to 7.7 kbar strongly alters water’s structure, producing an unusual pressure dependence of the shortest intermolecular distance and yielding results that align well with the known phase diagram.

Abstract

The pair correlation functions g(r) of liquid water obtained at pressures of up to 7.7 kbar at a constant temperature of 20 °C are discussed. A variety of evidence of the very strong effect of pressure on the structure of liquid water has been found. In particular, an unusual pressure dependence of the shortest intermolecular separation was observed. The results are interpreted in terms of fluctuations of the nearest environment, assuming that some of the structural configurations arising may be distinguished as preferred ones. The SIMPLEX procedure has been used to fit g(r) to the sum of correlation functions corresponding to the heavily destroyed structures of the solid phases of water. The results correlate with the phase diagram for water fairly well. This gives rise to an idea that water may be a suitable object for understanding the very nature of the liquid state.