Collision-Induced Microwave Absorption in Compressed Gases. II. Molecular Electric Quadrupole Moments

Abstract

A search for dielectric loss in the nondipolar gases, He, Ar, CH₄, SF₆, H₂, C₂H₆, N₂, and C₂H₄ was made at a frequency near 24 kMc and for densities not exceeding 100 amagat. For the first six gases, the loss factor was immeasurably small, less than 2×10^—7, at the maximum density. The loss observed in nitrogen and ethylene is attributed to transient dipoles induced by the molecular quadrupole fields during binary collisions. From the data on the quadrupolar gases, including previous results on CO₂, values of the quadrupole moments (or upper limits where no loss was observed) are derived which are in reasonable agreement with other estimates.