Gas mixture analysis by temperature-independent, multi-wavelength refractive mixing rules

The characterization of gaseous mixtures is an increasingly important issue in the fields of fuel analysis and aerosol research. Analyses by refractometry combined with refractive mixing rules are also powerful tools in this area. In this work a setup comprised by a six-laser interferometer and a vacuum system was projected and constructed in order to measure the refractivity of pure inert gases like N₂, CO₂, Ar and O₂ and to study the validity of the refractive mixing rules with binary mixtures of N₂ and Ar for different wavelengths. The light sources used in the experiments were a Hene laser (632.8 nm), a frequency-doubled diode-pumped Nd:YAG laser (532 nm) and four diode lasers emitting at 406.4 nm, 453 nm, 655.3 nm and 825 nm. The experimental refractivity data of the binary mixtures were compared with the theoretical ones obtained from a modified, temperature invariant, Gladstone-dale based refractive mixing rule, by introducing the parameter thermal refractivity (TR). The results obtained by the modified refractive mixing rule proposed by us for dry air were also compared with the refractive measurements of atmospheric air for the six wavelengths. In general the experimental results have shown good agreement with the theoretical predictions, and the dispersive character of the thermal refractivities point out to promising applications in evaluating gas mixtures.