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

Published: April 15, 2019


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


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
Pub Type: Journals
Created April 15, 2019