Ab initiosimulations of hot dense methane during shock experiments

Using density functional theory molecular dynamics simulations, we predict shock Hugoniot curves of precompressed methane up to 750.16em0ex000 K for initial densities ranging from 0.35 to 0.70 g0.16em0excm^-3. At 4000 K, we observe the transformation into a metallic, polymeric state consisting of long hydrocarbon chains. These chains persist when the sample is quenched to 3000.16em0exK, leading to an increase in shock compression. At 60000.16em0exK, the sample transforms into a plasma composed of many, short-lived chemical species. We conclude by discussing implications for the interiors of Uranus and Neptune and analyzing the possibility of creating a superionic state of methane in high pressure experiments.