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Article Dans Une Revue Icarus Année : 2023

Non-LTE spectroscopy of the tetradecad region of methane recorded in a hypersonic flow

Résumé

Laboratory spectroscopic data is essential for the modeling of hot exoplanet atmospheres, since molecules such as methane, a major component of hot-Jupiter-type exoplanet atmospheres, have a complex vibrational energy structure that makes computational predictions difficult at high temperatures for ro-vibrational transitions involving highly excited vibrational sates. To better inform line lists used in radiative transfer modeling, the ro-vibrational spectrum of methane has been recorded in the tetradecad region between 1.7 and 1.65 μm (5880–6060 cm−1) through non-local thermodynamic equilibrium (non-LTE) cavity ringdown spectroscopy (CRDS). Non-LTE conditions, characterized by a low rotational temperature (∼39 K) and a high vibrational temperature (up to 1130 K), have been obtained by hypersonic expansion of a pre-heated mixture of argon and methane in a contoured Laval nozzle. The high vibrational temperature increases the intensity of new hot bands, while the very low rotational temperature greatly simplifies their rotational structure, thus facilitating their identification. A close comparison of the recorded CRDS data to the TheoReTS database reveals both inefficient vibrational relaxation between polyads and efficient vibrational relaxation between vibrational states forming a polyad. These effects result in an overpopulation of the lowest vibrational energy level of each polyad, an effect not widely currently incorporated in non-LTE radiative transfer models. A series of new hot band transitions originating from the pentad and octad polyads were assigned and are provided as a line list for use in future databases. © 2023 Elsevier Inc.
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Dates et versions

hal-03975194 , version 1 (31-03-2023)

Identifiants

Citer

E. Dudás, B. Vispoel, Robert R. Gamache, Michael M. Rey, V.G. Tyuterev, et al.. Non-LTE spectroscopy of the tetradecad region of methane recorded in a hypersonic flow. Icarus, 2023, 394, pp.115421. ⟨10.1016/j.icarus.2022.115421⟩. ⟨hal-03975194⟩
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