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Absorption of methane broadened by carbon dioxide in the 3.3 μm spectral region: From line centers to the far wings

Abstract : This work studied the infrared absorption of methane broadened by carbon dioxide, which can contribute to the radiative budget of CO2-dominated atmospheres. Fourier transform absorption spectra of CH4 perturbed by CO2 were recorded in the 3.3 μm spectral region, at room temperature and total pressures ranging from 3 to 25 bars. These experimental data were modeled using a theoretical approach taking collision-induced line mixing into account. Comparisons between measured and calculated spectra demonstrate that the proposed model is capable of accurately representing the absorption of methane broadened by collisions with CO2, from line centers to the far wings. For practical applications, this rigorous spectral modeling was used to derive a simple χ-factor model to represent the spectral shape of CO2-broadened CH4 line wings. Comparisons with experimental values show that, at room temperature, the proposed χ-factor reproduces the measured spectra to within 10% in the band wings where the absorption is mainly due to the far line wings, while the usual Lorentzian profile leads to relative differences several orders of magnitude larger. This line-shape correction was successfully validated through comparisons with heavily saturated spectra of the ν3 band of methane recorded at sub-atmospheric pressures.
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https://hal-insu.archives-ouvertes.fr/insu-03726886
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Submitted on : Tuesday, July 19, 2022 - 7:57:45 AM
Last modification on : Wednesday, August 3, 2022 - 3:57:59 AM

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H. Tran, J. Vander Auwera, T. Bertin, W. Fakhardji, O. Pirali, et al.. Absorption of methane broadened by carbon dioxide in the 3.3 μm spectral region: From line centers to the far wings. Icarus, 2022, 384, ⟨10.1016/j.icarus.2022.115093⟩. ⟨insu-03726886⟩

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