The tetragonal γ form exists at low temperatures below 44.5 K between about 0.3 GPa and 3 GPa pressure. The triple point for α/β/γ2 is at 0.47 GPa and 44.5 K. The space group of the γ phase is "P"42/"mnm" and its unit cell has lattice constants a=3.957 Å, c=5.109 Å at 20 K and 4000 bar. The 15N isotope converts at a pressure 400 atmospheres lower to the γ form than natural nitrogen, at 20 K. In the γ form, nitrogen molecules appear to have the shape of a prolate spheroid, 4.34 Å in the long dimension, and 3.39 Å in the short diameter. The boundary of the molecule appears at an electron density of 0.0135 eÅ−3. The molecules line up in rows end to end diagonally on the ab plane. These rows stack side by side with molecules offset by half their length to form layers in the (001) plane, perpendicular to the c-axis. Layers stack on top of each other each rotated by 90° compared to the plane below. Coordinates of atoms in the unit cell are given by (x,x,0),(-x,-x,0),(+x,-x,),(-x,+x,) with x=r/a and r=interatomic distance in nitrogen molecule, = 1.10 Å. (unit cell dimension as above a=3.957 Å). The molecules can vibrate up to 10° on the ab plane, and up to 15° in the direction of the c axis.  δ-N2 has a triple point with β and γ Nitrogen at 2.3 GPa and 150 K. δ-N2 has a cubic structure with space group "pm"3"n" and eight molecules per unit cell. The lattice constant is 6.164 at 300 K and 4.9 GPa. This strucure is the same as for dioxygen (γ-O2) at 50 K. At room temperature and high pressure δ-nitrogen is ordered in its molecular orientation  Above the pressure of 2 GPa there is the lower temperature rhombohedral phase ε-N2 and above 80 K cubic δ-N2.