Precise modelling of infrared absorption by carbon dioxide is of primary importance for radiative transfer calculations in CO
-rich atmospheres like those of Venus and Mars. Despite various measurements and theoretical models dedicated to this subject, accurate data at different temperatures and pressures are still lacking in numerous spectral regions. In this work, using two Fourier Transform Spectrometers, we have measured spectra of pure CO
in a large spectral region range, from 750 to 8500 cm
at various densities (3–57 amagat) and temperatures (230–473 K). Comparisons between measured dipolar absorption bands and spectra calculated with the widely used Lorentz line shape show very large discrepancies. This result is expected since the Lorentz approach neglects line-coupling effects due to intermolecular collisions which transfer absorption from the wings to the band center. In order to account for this effect, a theoretical approach based on the impact and Energy Corrected Sudden approximations has been developed. Comparisons of this model with numerous laboratory spectra in a wide range of pressure, temperature and spectral domain show satisfactory agreements for band centers and near wing regions where the impact approximation is valid. However, as expected, due to the breakdown of the impact approximation, the model fails when considering far wing regions. In the absence of precise models accounting for line-mixing
finite collision duration (non impact) effects, empirical approximations are proposed in order to model the far wings.
Papers with the following subject areas are suitable for publication in the Journal of Quantitative Spectroscopy and Radiative Transfer:
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We present experimental results on the absorption by CO2-N2 mixtures in the 4.3 μm region. Measurements have been made in the 300–800 K and 0–60 bar ranges; these are in good agreement with previous determinations below 296 K. Frequency- and temperature-dependent factors χ are introduced in order to account for the subLorentzian behavior of the CO2 far line-wings. Their dependences on temperature are deduced from experimental results beyond the 4.3μm band-head in the 193–773 K range for both CO2-CO2 and CO2-N2 and fitted by simple analytical functions. Comparisons are presented between experimental and theoretical spectra on both the low- and high-frequency sides of the band (2100–2600 cm-1 range). It is shown that calculations using χ factors are inaccurate near line-centers at elevated pressures.
