Transition of liquid water to the supercritical state

Abstract

As was a long time believed, liquid and its gas can be distinguished one from another, if only they exist simultaneously below the critical point. This is because there is seemingly no qualitative difference between these two states. So there should not be a difference between a liquid and dense supercritical fluid. However, many experimental facts about water, cast doubt on this viewpoint. Especially interesting appears the enigmatical behavior of experimental pair correlation functions at the transition of liquid water to the supercritical state. Here we present a qualitative model for the transition based on the experimental data only. It is shown that the probability of hydrogen bonding approaches the percolation threshold near the critical isotherm. This means that the infinite cluster of hydrogen bonded molecules, which is characteristic for the liquid water, cannot exist in the supercritical fluid. The explanation of observed phenomena in terms of the percolation theory gives rise to a new conception of the transition of liquid water into the supercritical state. It also sheds light on the structure of the dense supercritical fluid and interrelation between all fluid states.