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

Laser refractometers are approaching accuracy levels where gas pressures in the range 1 Pa < p < 1 MPa inferred by measurements of gas refractivity at a known temperature will be competitive with the best existing pressure standards and sensors. Here, the authors 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. The authors give values of the coefficients c 1 , c 2 , c 3 for six gases: Ne, Ar, Xe, N 2, CO 2, and N 2 O. For each gas, the resulting molar polarizability A R ≡ 2 R T 3 c 1 has a standard uncertainty within 16 × 10 − 6 ⋅ A R. In these experiments, pressure was realized via measurements of helium refractivity at a 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 them 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. Laser refractometers are approaching accuracy levels where gas pressures in the range 1 Pa < p < 1 MPa inferred by measurements of gas refractivity at a known temperature will be competitive with the best existing pressure standards and sensors. Here, the authors 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. The authors give values of the coefficients c 1 , c 2 , c 3 for six gases: Ne, Ar, Xe, N 2, CO 2, and N 2 O. For each gas, the resulting molar polarizability A R ≡ 2 R T 3 c 1 has a standard uncertainty within 16 × 10 − 6 ⋅ A R. In these experiments, pressure was realized via measurements of helium refractivity at a known temperature: for He, the relationship between pressure and refractivity is known through...