A quantum mechanical calculation is given for collision-induced absorption in the infrared and far-infrared spectral regions for mixtures consisting of symmetrical diatomic molecules and rare-gas atoms. The induced moment consists of a short-range overlap term and a long-range quadrupole term. Near molecular transition lines, the quadrupole term gives the main contribution to the absorption, while in the far wings, the overlap term is dominant. The H2He, H2Ar, and N2Ar systems are considered, and an estimate is given of the absorption coefficient near 10 millimicrons for N2N2 systems. 53 pp. Ref.