Carbon dioxide shock and reshock equation of state data to 8 Mbar: Experiments and simulations

Abstract

We present density functional theory (DFT) simulations and shock-reshock experiments for liquid carbon dioxide (CO${}_{2}$) in the range 100 to 800 GPa. The simulations support the previously suggested dissociation threshold around 50 GPa [W. J. Nellis et al., J. Chem. Phys. 95, 5268 (1991)] for shocked liquid CO${}_{2}$ and describe a very steep Hugoniot past dissociation. We performed the shock-reshock experiments using the Sandia Z machine. The Z machine magnetically accelerated aluminum flyer plates to shock compress cryogenic liquid CO${}_{2}$ to 550 GPa and attained reshock states up to 840 GPa. The plate impact experiments combined with well-characterized impedance matching standards and laser velocimetry results in high-accuracy measurements of the principal Hugoniot and reshock states of liquid CO${}_{2}$. The experimental results validated the DFT simulations at extreme conditions and the combination of experiment and DFT provide reliable data for evaluating existing and constructing future wide-range equations of state models for molecular compounds such as CO${}_{2}$.