Collision induced microwave absorption is reported in pure CO2, and CO2-Ar, CO2-CH4 mixtures in the 70 G H z (2.3 cm-1) region at a temperature of 22°C, using a sensitive cavity technique previously described. The results in pure CO2 in the very low density region from 5 to 30 amagat accurately establish the dependence of the loss on the square and cube of the density, and the relaxation times are calculated. The experimental results agree well with previously reported lower frequency data at 0.3-0.8 cm-1 which establishes the linear dependence on frequency of the absorption up to 2.3 cm-1. There is also good agreement with an extrapolation of higher frequency infrared results of Ho et al. The relaxation times associated with the two and three body collisions are shown to be nearly equal at room temperatures with T~ = 0.84 x 10-12 s and T~ = 1.0 x 10-12 S. Higher order dependence on the density is observed for the CO2-Ar and CO2-CH4 mixtures. The results are compared with earlier low frequency measurements at 0.8 cm-1 and with the theory of Maryott and Kryder, taking account of correction terms in the dielectric virial coefficient according to Bose and Cole.
