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(Formula presented)(Formula presented) local vibrational mode is used to precisely calibrate the pressure. For all measured pressures we also observe the (Formula presented) vibrational mode of (Formula presented) impurities. For pressures greater than 1.9 GPa, a peak appears which we attribute to a N-N stretch mode of nitrogen in the ɛ phase. The single peak is consistent with previous x-ray and Raman studies which suggest that ɛ-(Formula presented) has a structure which belongs to the rhombohedral space group R3¯C.