NIST Authors in **Bold**

Author(s): | Michael R. Moldover; E May; James W. Schmidt; |
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Title: | The Electric And Magnetic Susceptibilities Of Gaseos Oxygen: Comparisons Of New Measurements and Modern Theory |

Published: | September 25, 2008 |

Abstract: | We used a cross capacitor to measure the relative dielectric permittivity ε_{r} of O_{2} 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, υ_{r}(f, p, T), with an uncertainty of less than 1 % of (υ_{r} – 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: χ_{meas,M000}=χ_{M}(0,0,293.15 K), and the second magnetic virial coefficient, b_{υ}. 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 χ_{meas,M000} = (42.92 {plus or minus} 0.06)×10^{–9} m^{3} mol^{–1} and b_{υ}=(–1.8 {plus or minus} 0.5) cm^{3} mol^{–1}. The result for χ_{meas,M000} is consistent with a recent ab initio calculation: χ_{meas,M000}/χ_{calc,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} χ_{meas,M000}/χ_{calc,M000} {less than or equal to} 1.019. Our measurements of ε_{r} determine the static molecular dielectric polarizability of oxygen: (1.7456 {plus or minus} 0.0003)×10^{–40} C^{2} m^{2} mol^{–1}, which deviates by +0.7 % and –0.1 % from two recent ab initio calculations. |

Citation: | Physical Review A (Atomic, Molecular and Optical Physics) |

Volume: | 78 |

Issue: | 9/25/2008 |

Pages: | pp. 032522-1 - 032522-15 |

Keywords: | electric susceptibility; dielectric constant; magnetic permeability; magnetic susceptibility; relative magnetic permeability; oxygen; paramagnetism; refractive index; |

Research Areas: | Gas Metrology, Physical Properties, Chemical Engineering & Processing, Standard Reference Data, Chemistry, Fluids, Thermodynamics, Measurements |