Shock-Induced Cooling in Liquid Nitrogen Revisited

Evolution of nitrogen under shock compression up to 100 GPa is revisited via molecular dynamics simulations using a machine-learned interatomic model. Our model is shown capable of recovering the structure, dynamics, speciation and kinetics in hot compressed liquid nitrogen predicted by first- principles molecular dynamics, as well as the experimentally determined principal shock Hugoniot. We find that a purely molecular dissociation description of nitrogen chemistry provides an incomplete picture, and that short oligomers form in non-negligible quantities; no evidence is found for shock- induced cooling upon re-shocking.