Publication Citation (NIST authors in bold)
Authors:	Schmidt, J. W., Moldover, M. R., May, E.
Title:	Reference measurements of Hydrogen's Dielectric Permittivity
Published:	August 10, 2009
Abstract:	We used a quasi-spherical cavity resonator to measure the relative dielectric permittivity {epsilon}r of H2 at frequencies from 2.4 GHz to 7.3 GHz, at pressures up to 6.5 MPa, and at the temperatures 273 K and 293 K. The resonator was calibrated using auxiliary measurements of {epsilon}r({I}p{/I},{I}T{/I}) for helium together with the accurate {I}ab initio{/I} values of helium's dielectric permittivity. The measurements determine accurate values of hydrogen's molecular electric polarizability and its temperature dependence. At 273 K, we obtained {alpha}{epsilon},H2 = (8.9568{plus or minus}0.0008) {multiply}10-41 F m2, which agrees with the value (8.9566{plus or minus}0.0026) {multiply}10-41 F m2 that was obtained by combining Rychlewski's {I}ab initio{/I} calculations with estimates of rotational level populations. (All uncertainties reported here are one standard uncertainty.) Our results yield the temperature dependence {I}d{alpha}{/I}{epsilon},H2/{I}dT{/I}={I}{alpha}{/I}{epsilon},H2{multiply}(1.1{plus or minus}0.3){multiply}10-5 K-1, which agrees with the calculated value 1.0{multiply}10-5 K-1. Our data also determine hydrogen's second dielectric virial coefficient, {I}b{/I}{epsilon},H2 = (0.03{plus or minus}0.05) cm3 mol-1, a property that has not yet been calculated.
Citation:	Molecular Physics
Volume:	107
Issue:	15
Pages:	pp. 1577-1585
Keywords:	dielectric constant, dielectric permittivity, helium, hydrogen
Research Area:	Chemistry, Chemical Engineering & Processing, Thermophysics, Physical Properties, Gas Metrology, Standard Reference Data, Energy, Hydrogen, Standards, Measurement Standards, SRD (Fluids), SRD (Thermophysical & Thermochemical), Transportation, Fuels;
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