Article Dans Une Revue Journal of Quantitative Spectroscopy and Radiative Transfer Année : 2025

Analysis of a non-LTE hypersonic spectrum of methane between 5880 and 6220 cm−1

Résumé

The SMAUG device is used to thermally populate the vibrational states of the methane molecule and depopulate its rotational states through its supersonic expansion in argon. The methane molecule is probed during expansion by cavity ringdown spectroscopy (CRDS) between 5880 and 6220 cm−1. The laser beam passes through both the isentropic core of the flow, characterized by a very low rotational temperature of 40.4 ± 0.8 K, and the hotter boundary layers surrounding it, which are characterized by an average rotational temperature of 364.3 ± 7.7 K. Analysis of the spectrum reveals that the vibrational population does not follow a Boltzmann distribution. A special procedure is developed to assign an effective vibrational temperature to each vibrational state, ranging from 532.4 ± 32.2 to 1112.0 ± 81.7 K for molecules in the isentropic core, and from 811.6 ± 43.1 to 851.8 ± 45.6 K for those in the shear layer. Only the first vibrational states of each methane polyad remain significantly populated leading to detectable transitions. A total of 2347 transitions from the cold gas of the isentropic core and from the warmer gas of the boundary layers are assigned from a new ab initio effective model and 749 are confirmed by lower state combination differences (LSCD). Among these transitions, 694 originates from cold bands and 1653 from hot bands starting from vibrational states ν4, ν2 (dyad), 2ν4 (pentad) and 3ν4 (octad).

Fichier principal
Vignette du fichier
1-s2.0-S0022407325003188-main.pdf (2.83 Mo) Télécharger le fichier
ScienceDirect_files_26Jan2026_11-16-42.568.zip (155.37 Ko) Télécharger le fichier
Origine Publication financée par une institution
Licence

Dates et versions

hal-05343238 , version 1 (03-11-2025)
hal-05343238 , version 2 (18-11-2025)
hal-05343238 , version 3 (26-01-2026)

Licence

Identifiants

Citer

Lyam Rolland-Roignant, Eszter Dudás, Nicolas Suas-David, Michael M. Rey, Samir Kassi, et al.. Analysis of a non-LTE hypersonic spectrum of methane between 5880 and 6220 cm−1. Journal of Quantitative Spectroscopy and Radiative Transfer, 2025, 347, pp.109656. ⟨10.1016/j.jqsrt.2025.109656⟩. ⟨hal-05343238v3⟩
1957 Consultations
209 Téléchargements

Altmetric

Partager

  • More