METALLIZATION AND DISSOCIATION OF FLUID HYDROGEN AND OTHER DIATOMICS AT 100 GPa PRESSURES

Abstract

Dynamic compression of diatomic liquids using both single-shock (Hugoniot) and multiple-shock (reverberating-shock) compression achieves pressures which range up to a few 100 GPa (Mbar), densities as high as tenfold of initial liquid density in hydrogen, and temperatures up to several 1000 K. Single-shock compression produces substantial heating, which causes a limiting compression. Multiple-shock compression is quasi-isentropic, which achieves lower temperatures and higher densities than single shocks, and has no limiting compression. Diatomic fluids have universal behaviors under dynamic compression. Under multiple-shock compression, these fluids undergo density-driven nonmetal-metal Mott transitions, probably in the monatomic state, with common density scaling at ∼100 GPa. Under single-shock compression, these fluids have essentially the same Hugoniot in velocity space. D₂ undergoes temperature-driven dissociation to a poor metal at ∼50 GPa. These results provide insight into which of the two published D₂ Hugoniots is probably correct.

Keywords:

• Hydrogen
• Diatomics
• Hugoniot
• Quasi-isentrope
• Mott transition