Collision-Induced Microwave Absorption in Compressed Gases. I. Dependence on Density, Temperature, and Frequency in CO2

Abstract

Measurements of the dielectric loss by a resonant cavity technique at 9 and 24 kMc/sec are reported for CO2 for densities up to 100 amagat and 25°C. Some additional data are reported at elevated temperatures. The loss, which increases in proportion to the frequency and very nearly as the square of the density, is attributed to transient dipoles induced by the molecular electric quadrupole fields during molecular collisions. A theoretical analysis including the line shape is made to relate the loss to the pertinent molecular parameters and to permit an intercomparison with precise data available on the second dielectric virial coefficient. It is concluded that the microwave loss in quadrupolar gases may provide a sensitive method of getting information on the molecular quadrupole moments.