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

Direct laser heating of molecular N-2 to above 1400 K at 120-130 GPa results in the formation of a reddish amorphous phase and a transparent crystalline solid above 2000 K. 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 eta 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 70 GPa, 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.