Temperature, density, and perturber dependences of absorption of the 3.39 µm He-Ne laser by methane

We present an experimental and theoretical study of the absorption of the IR He-Ne laser (3.39 µm) by Ch₄. Shocktube measurements were made for mixture of CH₄with Ar, N₂, and O₂in wide density and temperature ranges. Calculations were made by using the available spectroscopic data on CH₄absorption lines. Comparison between experiments and calculations show that the theoretical predictions are accurate for all densities up to the temperature of 1200 K. At 2000 K, the calculations fail, probably due to insufficient knowledge of hot-band lines. Furthermore, the present study shows that mixture of CH₄with Ar, O₂, and N₂lead to absorptions which are similar (within experimental error), as is confirmed by the theoretical model.