A previously reported quantum spectral theory for evaluating the far-infrared absorption spectrum of diatomic molecules in rare-gas fluids [J. Chem. Phys. 103, 9161 (1995)] is applied to the case of a N-2-Xe gaseous mixture at room temperature and a very low concentration of N-2 (0.85% ). The theoretical line shape is built by considering the two leading electric multipolar induced contributions. From comparison between theoretical and experimental spectra an estimation of the quadrupole and hexadecapole moments of N-2 is given.