Raman, infrared, and x-ray evidence for new phases of nitrogen at high pressures and temperatures

We report the existence and characterization of a distinct class of molecular phases of solid nitrogen at high pressures and temperatures by Raman scattering, infrared absorption, and powder synchrotron x-ray diffraction. The most remarkable is a phase (θ) which is characterized by strong intermolecular interactions and infrared vibron absorption. A second lower-pressure phase (ι) is diatomic with orientationally equivalent molecules. Both phases can be quenched to room temperature and are observed over a wide P-T range from 20 to 100 GPa and 30 to 1000 K. The results suggest a major revision of the phase relations of nitrogen at high pressures and temperatures.