Far-infrared spectra of N2-Ar alloys

The far-infrared spectra of (N₂)_1-xAr_x solid mixtures have been studied at 18 K and p=0 for 0<x<0.25. At x=0, in addition to the phonon peaks T⁽¹⁾_u and T⁽²⁾_u, the combination bands recently observed at high pressure have been detected. In the alloy, the width of T⁽¹⁾_u increases with x while its central frequency slowly decreases. In the β phase (x=0.25) a translational mode still exists, which can be derived from the T⁽¹⁾_u mode of the α phase. T⁽²⁾_u is nearly insensitive to the concentration of impurities, but it disappears at the α-β transition. A concentration x=0.05 of Kr atoms is found to enhance the intensity of absorption in solid N₂ by a factor of 5.