Hydrogen at megabar pressures and the importance of ortho-para concentration

Abstract

Hydrogen and its isotopes are discussed, showing the known phase diagrams at high pressures, with emphasis on efforts to observe the insulator-metal transitions. The role that the ortho-para concentration has played in the challenging effort to produce metallic hydrogen is discussed, showing recent NMR results on the determination of the conversion rate constant, important for knowing the state of a sample at high pressure.