Refractive index of shock-compressed liquid nitrogen up to 29 GPa

ABSTRACT We report the equation of state and optical properties of shock-compressed liquid nitrogen (LN2) by using a two-stage light-gas gun at pressure up to 29 GPa. Laser velocimetry measurements were used to investigate the transparency and refractive index of shocked LN2 as a function of density. As the density increased with increasing pressure and temperature (13–25 GPa), the refractive index increased up to 27% of pre-shot index of LN2. Evidently, such extreme conditions had no major influence on molecules, and no such dissociation was observed up to 25 GPa. The polarizability slightly decreased and thus supported the existence of intact diatomic molecular nitrogen. At 29 GPa, shocked LN2 dissociated, showing that it probably changed to a highly reflecting fluid. Altogether, these experiments showed how the density affects the refractive index without any change in chemical bonding and allocates the condition at which the temperature-driven dissociation takes place.