Dielectric Constants of Imperfect Gases. I. Helium, Argon, Nitrogen, and Methane

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Abstract
Measurements from 1 to 100 atm have been made at one or more temperatures between —30° and 70°C by a special transformer ratio arm bridge operating at 10 kc; derived values of the Clausius‐Mossotti function are of sufficient precision (0.1%) to justify comparison with theoretical pair fluctuation, polarizability and multipole moment interaction effects at higher densities. Helium shows a decrease of 0.3% and argon an increase of 0.1% in C‐M at 100 atm, while nitrogen and methane show somewhat larger positive effects, especially at lower temperatures. A decreased effective polarizability of atom pairs at small distances is discussed as a possible explanation of the data for helium and argon, while the effect in nitrogen is consistent with quadrupole‐induced dipole moments of pairs. A theory of octupole‐induced dipole interactions is shown to be capable of explaining the methane results with plausible estimated values of the octupole moment.