Dynamics in supercritical fluid water

Abstract

Recently we have developed a new microwave spectroscopy technique in the frequency range up to 40 GHz and measured the dielectric relaxation time for supercritical water and heavy water. The dielectric relaxation time in both liquid and decreases rapidly with increasing temperature and jumps to a large value at the liquid-gas transition. The relaxation time of is longer than that of in the liquid state, and the difference becomes smaller with decreasing density in the gaseous state. Based upon the observation that the dielectric relaxation time becomes fairly long in the dilute limit, we propose that the dielectric relaxation in the gaseous state is governed by the binary collision of molecules. In the liquid state, on the other hand, the contribution of the molecules that are incorporated in the hydrogen-bond network to the dielectric relaxation should be taken into account. The relation between and the viscosity, as well as the relation between and the diffusion constant, are also discussed in the whole fluid phase.