Refractive index measurements have been carried out on fluid xenon isochores from 299K to the coexistence temperatures. The mean value of the Lorentz-Lorenz function in the range 5-15 k mol m-3 is 10.524 mu m3 mol-1 ( lambda =589.3 nm). The results indicate that (a), the Lorentz-Lorenz function for xenon does not vary by more than +or-0.5% throughout the fluid range, (b) there is no evidence for a large anomaly near Tc, and (c) the temperature dependence of the Lorentz-Lorenz function is small.

https://iopscience.iop.org/article/10.1088/0022-3719/4/15/010/pdf

Temperature and density dependence of the Lorentz-Lorenz function of fluid xenon near the critical region

The refractive index (n) or dielectric constant (e) of a dielectric material is a function of the thermodynamic state. For a non-polar substance, in which the constituent molecules do not possess a permanent dipole moment, e = n 2 (at the same frequency), and the dielectric constant is related to the molecular polarizability α, Avogadro’s number N A, and the density ρ, by the Clausius-Mossotti relation (CM).

Relation of the Dielectric Constant and the Refractive Index to Thermodynamic Properties

An optical cell is described, suitable for measuring the temperature dependence of the refractive index n of a fluid at constant density near Tc. Based on the spectroscopic method of minimum deviation, the method determines n to ?0?012%.

B L Smith

Papers

Optical cell for isochoric measurements of refractive index near the critical region