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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The shapes of the extreme wings of self-broadened CO2(lines have been investigated)in three spectral regions near 7000, 3800, and 2400 cm-1. Absorption measurements have been made on the high-wavenumber sides of band heads where much of the absorption by samples at a few atm is due to the extreme wings of strong lines whose centers occur below the band heads. New information has been obtained about the shapes of self-broadened CO2 lines as well as CO2 lines broadened by N2, O2, Ar, He, and H2. Beyond a few cm-1 from the line centers, all of the lines absorb less than Lorentz-shaped lines having the same half-widths. The deviation from the Lorentz shape decreases with increasing wavenumber, from one of the three spectral regions to the next. The absorption by the wings of H2- and He-broadened lines is particularly low, and the absorption decreases with increasing temperature at a rate faster than predicted by existing theories.
