Infrared absorption of solid nitrogen at high pressures

We have observed infrared absorption peaks in solid nitrogen at hydrostatic pressures as high as 7 GPa at liquid-helium temperatures. The shift in the AlSb:¹²{C}Sb$ local vibrational mode is used to precisely calibrate the pressure. For all measured pressures we also observe the ${{ν}}₃$ vibrational mode of ${CO}₂$ impurities. For pressures greater than 1.9 GPa, a peak appears which we attribute to a N-N stretch mode of nitrogen in the {ε} phase. The single peak is consistent with previous x-ray and Raman studies which suggest that {ε}-N₂ has a structure which belongs to the rhombohedral space group R3{}C. {} 1996 The American Physical Society.