Earth and Planetary Science

The Problem of CO2 Reabsorption in Emission Spectra

Svatopluk Civiš

J. Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova, Prague, 18223, Czech Republic

Adam Pastorek

Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia, 23529, United States of America

Sergei N. Yurchenko

Faculty of Mathematical and Physical Sciences, University College London, Gower Street, London, WC1E6BT, United Kingdom

DOI: https://doi.org/10.36956/eps.v2i1.836

Received: 4 April 2023; Revised: 26 April 2023; Accepted: 27 April 2023; Published Online: 17 May 2023

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Abstract

The authors present a detailed explanation for selective reabsorption by the CO₂ ν₃-band when passing its optical emission through an atmospheric-pressure air column (60 cm long, 410 ppm CO₂) connecting a microwave-discharge cell and the entrance window of a high-resolution Fourier Transform spectrometer. The CO₂ band shapes are explained with a two-temperature model of emission and foreground absorption. Selective CO₂ atmospheric reabsorption is a common effect in optical emission measurements. It primarily affects the fundamental infrared bands, which comprise the main part of the missing laboratory emission and must be taken into account in (exo)planetary atmospheric models.

Keywords: Reabsorption, Carbon dioxide, FTIR spectroscopy, Vacuum vs air measurement

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