Room temperature Raman scattering studies of external and internal modes of solid nitrogen at pressures 8≤<i>P</i>≤54 GPa

Abstract

Raman spectra of solid nitrogen were studied from 8 to 54 GPa at room temperature. Between 8 and 16 GPa three out of four possible lattice modes of the δ–N2 phase were observed. Above 16 GPa up to eight lattice modes can be distinguished, seven of which correspond to lattice modes observed at 15 K in the ε–N2 phase. Branching of existing lattice and vibronic modes above 20 GPa and above 40 GPa indicate additional slight structural modifications. The observed pressure shift of vibrons of the 14N–15N isotopic species appears to favor factor group effects instead of bond weakening to be responsible for the downward shift of one vibronic mode at higher pressures.