Vibrational dynamics of solid molecular nitrogen to megabar pressures

We report the results of Raman and synchrotron infrared absorption measurements of several molecular phases of solid nitrogen to pressures above 100 GPa (300 K). Low-temperature vibrational spectra to 45 GPa are also presented. The changes in Raman and infrared spectra at 60 GPa and 300 K are interpreted as arising from the ε→ζ transition reported at low temperature. The character of splitting of the Raman vibron ν2 observed at 25 GPa and low temperatures differs from that previously reported, a difference that we ascribe to different experimental procedures employed and metastability of the low-temperature phase.