Type:		Journal, Article
Title:		Fluid hydrogen at high density: Pressure ionization
Author(s):		Saumon, D.; Chabrier, G.
Date:		1992/08/15
Abstract:		In an earlier paper [Phys. Rev. A 44, 5122 (1991)], we presented a Helmholtz-free-energy model for nonideal mixtures of hydrogen atoms and molecules. In the present paper, we extend this model to describe an interacting mixture of H2, H, H+, and e- in chemical equilibrium. This general model describes the phenomena of dissociation and ionization caused by pressure and temperature effects, as encountered in astrophysical situations and high-pressure experiments. The present model is thermodynamically unstable in the pressure-ionization regime and predicts the existence of a plasma phase transition with a critical point at Tc=15 300 K, Pc=0.614 Mbar, and ρc=0.35 g/cm3. The transition occurs between a weakly ionized phase and a partially (≊50%) ionized phase. Molecular dissociation and pressure ionization occur in the same narrow density range; atoms play a minor role in pressure ionization. In the high-density phase, complete pressure ionization is reached gradually. The sensitivity of the coexistence curve and of the critical point to model parameters and assumptions is discussed in detail.
Publisher:		American Physical Society
Journal (full):		Physical Review A
Volume:		46
Issue:		4
Start Page:		2084
End Page:		2100
Link:		http://link.aps.org/doi/10.1103/PhysRevA.46.2084