Shock Compression of Deuterium near 100 GPa Pressures

The shock-compression curve (Hugoniot) of D₂ near 100 GPa pressures (1 Mbar) has been controversial because the two published measurements have limiting compressions of fourfold and sixfold. Our purpose is to examine published experimental results to decide which, if either, is probably correct. The published Hugoniot data of low-Z diatomic molecules have a universal behavior. The deuterium data of Knudson et al. (fourfold limiting compression) have this universal behavior, which suggests that Knudson et al. are correct and shows that deuterium behaves as other low-Z elements at high temperatures. In D₂, H₂, N₂, CO, and O₂, dissociation completes and average kinetic energy dominates average potential energy above ~60 GPa. Below ~30 GPa, D₂, H₂, N₂, CO, and O₂ are diatomic. D₂ dissociation is accompanied by a temperature-driven nonmetal-metal transition at ~50 GPa.