Properties of high density gaseous nitrogen under shock compression in hemispherical geometry

Recent investigations of liquid nitrogen properties under shock compression show compression limit of 4.2 close to of ideal gas $\sigma =$ 4 in pressure region 100 -- 330 GPa and demonstrate an unusual Hugoniot pressure -- density dependence similar to isochoric compression. We performed two experiments with gaseous nitrogen with initial density $\rho _{0} =$ 0.8 g/cm$^{3}$ to confirm previous data on liquid nitrogen. The experiments were conducted using HE shock wave generators of hemispherical geometry. We obtain Hugoniot pressures (190 $\pm$ 5) and (226 $\pm$ 5) GPa, compressions (4,64 $\pm$ 0,47) and (4,42 $\pm$ 0,36), temperatures (37500 $\pm$ 5800) and (45900 $\pm$ 9300) K. Experimental data on gaseous nitrogen agree with that on liquid nitrogen and modified model of compressible covolume.