Pressure-Induced Microwave Absorption of Nonpolar Gases

A theory is developed which describes the microwave absorption of nonpolar gases. The contributions arising from collisionally induced absorption and from dimers are evaluated separately. It is found that at low enough temperatures the absorptive properties of such gases are dominated by the dimeric states. This accounts for the observed anomalous temperature dependence of the absorption coefficient. A comparison of the theoretical predictions with experimental data on carbon dioxide and nitrogen yields good agreement.