Absolute Equation of State Measurements on Shocked Liquid Deuterium up to 200 GPa (2 Mbar)

We present results of the first measurements of density, shock speed, and particle speed in liquid deuterium compressed by laser-generated shock waves to pressures from 25 to 210 Gpa (0.25 to 2.1 Mbar). The data show a significant increase in ${\mathrm{D}}_{2}$ compressibility above 50 Gpa compared to a widely used equation of state model. The data strongly suggest a thermal molecular dissociation transition of the diatomic fluid into a monatomic phase.