Royal, Damian Derek; (2000) Dielectric constants of simple gases determined using microwave cavity resonators. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The dielectric constants of simple, non-polar gases have been measured with fractional uncertainties on the order of ±1 ppm using two microwave cavity resonators. A spherical resonator with internal radius of 40 mm was used to make measurements on argon at four temperatures between 215 K and 300 K, nitrogen at 300 K, the mixture (0.5 Ar + 0.5 N₂) at 300 K, and xenon at eight temperatures between 189 K and 360 K, for pressures below 1 MPa. A newly-designed cylindrical resonator, with internal radius of 9.5 mm and length 20.0 mm, was used to make measurements on nitrogen at ten temperatures between 243 K and 323 K, for pressures up to 4.015 MPa. The ε(p, T) measurements were combined with published (p, Vm, T) virial coefficients and fitted to a form of the density-explicit expansion of the Clausius- Mossotti function to obtain estimates of the dielectric virial coefficients. The first dielectric virial coefficients were always in excellent agreement with published values (generally within 0.1 %). The second dielectric virial coefficients of xenon tended to be higher than the few published results although they generally agreed within the combined uncertainties, whilst the second dielectric virial coefficients of nitrogen were in good agreement with published results and enabled the determination of the quadrupole moment of nitrogen in superb agreement with values in the literature. The sphere measurements were also fitted to obtain estimates of the second (p, Vm, T) virial coefficients in very good agreement with the most recently published results.

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