| Abstract: |
We used a cross capacitor to measure the relative dielectric permittivity εr of O2 at 273 K, 293 K, and 323 K and at pressures up to 6.5 MPa. Simultaneously we measured oxygen's complex refractive index n using a quasi-spherical cavity resonator at frequencies between 2.4 GHz and 7.3 GHz. The combined results from these measurements determine oxygen's frequency-dependent, relative magnetic permeability, υr(f, p, T), with an uncertainty of less than 1 % of (υr – 1) at pressures above 2 MPa. Regression of these data to a model for oxygen's impact-broadened microwave spectrum allowed us to determine two quantities that are, in principle, amenable to calculation: the molar magnetic susceptibility in the limits of zero-pressure and zero-frequency: χmeas,M000=χM(0,0,293.15 K), and the second magnetic virial coefficient, bυ. With oxygen's electronic g-factor constrained to 2.0039 {plus or minus} 0.0003 (the value known from laser magnetic resonance, EPR and molecular beam experiments), we obtained χmeas,M000 = (42.92 {plus or minus} 0.06)×10–9 m3 mol–1 and bυ=(–1.8 {plus or minus} 0.5) cm3 mol–1. The result for χmeas,M000 is consistent with a recent ab initio calculation: χmeas,M000/χcalc,M000 = 0.9998 {plus or minus} 0.0014. Our measurements of oxygen's magnetic susceptibility are the first made relative to the susceptibility of helium calculated ab initio. All previous measurements were made relative to the diamagnetic susceptibility of water. These previous measurements, published in 1943 or earlier, span the wider range 0.975 {less than or equal to} χmeas,M000/χcalc,M000 {less than or equal to} 1.019. Our measurements of εr determine the static molecular dielectric polarizability of oxygen: (1.7456 {plus or minus} 0.0003)×10–40 C2 m2 mol–1, which deviates by +0.7 % and –0.1 % from two recent ab initio calculations. |
| Research Areas: |
Gas Metrology, Physical Properties, Chemical Engineering & Processing, Standard Reference Data, Chemistry, Fluids, Thermodynamics, Measurements |
