Raman study of pressure-induced dissociative transitions in nitrogen

The pressure-induced intermolecular and intramolecular dissociation transitions in nitrogen have been investigated in this work. The experimental intermolecular dissociative transition pressures for solid molecular phases (β, δ, δloc, ε, ζ, ζ’, κ and η) have been carefully determined up to 136 GPa by high-pressure Raman spectroscopy, and the high-frequency Raman vibrons of molecular solids has been assigned by analyzing the local molecular polarization properties. We demonstrate that pressure-induced symmetry breaking leads to a series of solid molecular phases in nitrogen associated with a splitting of vibrons. The polymeric cg-N was synthesized at about 134 GPa and above 2000 K, and the pressure dependence of Raman mode for cg-N was studied in conditions of increasing pressure up to 172 GPa and decreasing pressure down to 46 GPa. The zero-pressure mode-Grüneisen parameter of the cg-N Raman A mode was also extrapolated to be 1.24 ± 0.02.