Raman Spectrum of Solid Nitrogen at High Pressures and Low Temperatures.

The Raman spectrum of the three known phases of solid nitrogen has been studied in the temperature range from 0 to 200 K and the pressure range from 0 to 10 Kbar. A novel method was used in that the sample was grown within a high pressure optical cell which constrained it to nearly isochoric conditions. This method allows the separation of temperature and volume effects. Two lines have been observed in the lattice region of the gamma-phase which are identified as Eg and B1g librational modes on the basis of frequency and relative intensity calculations. An asymmetrical line has been observed in the stretching region of this phase. Two very broad lines are found in the lattice region of the beta-phase. The low- and high-frequency lines are identified with translational and librational modes, respectively.