Collision induced microwave absorption is reported in pure N2, CO2, and H2 in the region of 2.3 cm−1. For N2 the results are taken at temperatures ranging from 208 to 333 K and at densities ranging from 50 to 300 amagat. The parts of the loss factor which are proportional to the square and the cube of the density are found to depend respectively on T−1.55±0.12 and T−2.56±0.44. These results are well explained by the theory which relates the virial coefficients and relaxation times to the loss factor. Both the two and three body relaxation times, τ2 and τ3 follow very closely a T−0.5 dependence. The ratio of τ2/τ3 is found to be 0.83. For CO2 the results are taken at temperatures ranging from 273 to 363 K and at densities ranging from 8 to 80 amagat. The parts of the loss factor which are proportional to the square and cube of the density depend respectively on T−3.08±0.05 and T−5.4±0.059. These results together with existing infrared results show that τ2 is nearly proportional to T−0.5 and the ratio τ2/τ3 is 0.91 at 296 K. An initial measurement is reported for collision induced absorption in H2. The results for all three gases have been compared to previously reported results in the low frequency region.