The collision induced far infrared spectrum of N2is evaluated by molecular dynamics using a model of quadrupole induced dipoles. The results for two high density, low temperature states (ϱ = 742 Amag,T= 81 K and ϱ = 610 Amag,T= 91 K) are compared with new measurements. The spectral line shapes show a faster decay at high frequency (v> 90 cm-1) than those given by experiment. The integrated absorption coefficient is shown to result from almost complete cancellation between two-, three-, and four-body contributions. The effect of the polarizability anisotropy on the integrated absorption and line shape is examined.