Line mixing and finite duration of collision effects in pure CO2 infrared spectra: Fitting and scaling analysis

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Abstract
We present experimental and calculated pure CO2 infrared spectra in the 2.0, 4.0, and 5.0 μm regions for pressures and temperatures in the 10–60 bar and 300–950 K ranges, respectively. Our measurements are in good agreement with previous ones. The inaccuracy of the Lorentzian model is demonstrated in both the wings and central regions of absorption bands. Models which account for line mixing within the impact approximation are also tested; they are based on nondiagonal relaxation operators built by using fitting laws and the energy corrected sudden scaling analysis. These approaches fail in modeling absorption in far wings, due to the breakdown of the impact approximation. Correction functions, which roughly account for the finite collision duration through a wave‐number‐dependent relaxation operator, are deduced from measurements beyond the ν3 bandhead. They enable accurate modeling of the P‐branch side of this band and have wave‐number and temperature dependences consistent with available data. Spectra at high densities in the 2.0 and 5.0 μm regions show that calculated absorptions are very sensitive to the amount of interbranch mixing. Good agreement with experimental results is obtained when intra‐ and interbranch line mixings are of the same order.

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