Transformation of molecular nitrogen to nonmolecular phases at megabar pressures by direct laser heating

Direct laser heating of molecular N₂ to above 14000.3em0exK at 120--1300.3em0exGPa results in the formation of a reddish amorphous phase and a transparent crystalline solid above 20000.3em0exK. Raman and x-ray data confirm that the transparent phase is cubic-gauche nitrogen (cg-N), while the amorphous phase could be an extension of the already known η phase. The reddish color of the amorphous phase, however, might also indicate the presence of NN bonds. The quenched amorphous phase is stable down to at least 700.3em0exGPa, analogous to cg-N. A chemophysical phase diagram is presented which emphasizes the difference between pressure- and temperature-induced transitions from molecular to nonmolecular solids, as found in other low Z systems.