Model for Shock-Compressed Liquid Deuterium

The equation of state of dense liquid deuterium has been calculated using a model in which the Helmholtz free energy is approximated as the composition average of the free energy of pure molecular and metallic hydrogen. The composition is determined by free energy minimization. Calculations for shock-compressed liquid deuterium are in good agreement with experiments to a pressure of 2.1 Mbar. At about 1 Mbar and 20000 K, liquid deuterium is 90 % dissociated and is a nearly liquid degenerate metal. The model predicts that molecular dissociation will lead to negative values of (P/T)v in the range 4000 K to 10 000 K and volumes below 7 cm/mol. This feature suggests the formation of covalently bonded species in the partially dissociated mixture.