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Measured relationship between thermodynamic pressure and refractivity for six candidate gases in laser barometry

Published

Author(s)

Patrick F. Egan, Jack Stone, Julia K. Scherschligt, Allan Harvey

Abstract

Laser refractometers are approaching accuracy levels where gas pressures in the range 1 Pa < p < 1 MPa inferred by measurements of gas refractivity at known temperature will be competitive with the best existing pressure standards and sensors. Here, we develop the relationship between pressure and refractivity p = c_1 * (n-1) + c_2 * (n-1)^2 + c_3 * (n-1)^3 + ..., via measurement at T = 293.1529(13) K and λ = 632.9908(2) nm for p < 500 kPa. We give values of the coefficients c_1, c_2, c_3 for six gases: Ne, Ar, Xe, N_2, CO_2, and N_2O. For each gas, the resulting molar polarizability A_R = 2 R T / (3 c_1) has a relative standard uncertainty within 16 x 10^-6 * A_R. In these experiments, pressure is realized via measurements of helium refractivity at known temperature: for He, the relationship between pressure and refractivity is known through calculation much more accurately than it can presently be measured. This feature allowed us to calibrate a pressure transducer in situ with helium, and subsequently use the transducer to accurately gage the relationship between pressure and refractivity on an isotherm for other gases of interest.
Citation
Journal of Vacuum Science & Technology A
Volume
37
Issue
3

Citation

Egan, P. , Stone, J. , Scherschligt, J. and Harvey, A. (2019), Measured relationship between thermodynamic pressure and refractivity for six candidate gases in laser barometry, Journal of Vacuum Science & Technology A, [online], https://doi.org/10.1116/1.5092185 (Accessed February 27, 2024)
Created April 14, 2019, Updated February 5, 2021