Measurements and predictions of H₂ pressure-broadening coefficients of CO₂ absorption lines for exoplanet atmosphere studies

¹ Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Université, École Normale Supérieure, Université PSL, École polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France
² Université de Tunis, Laboratoire de Spectroscopie et Dynamique Moléculaire, École Nationale Supérieure d’Ingénieurs de Tunis, 5 Av. Taha Hussein, 1008 Tunis, Tunisia
³ Univ Paris Est Créteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 23 January 2026
Accepted: 27 February 2026

Abstract

Accurate and comprehensive H₂ pressure-induced broadening data for CO₂ infrared lines over a wide temperature range are essential for modeling atmospheric opacity of exoplanets. However, available data are currently limited, some of which are affected by large uncertainties. In this work, H₂ pressure-induced broadening and pressure-shift coefficients were determined at room temperature for the entire ν₃ band of CO₂ in the 4.3 µm spectral region using a high-resolution Fourier transform spectrometer. In addition, requantized molecular dynamics simulations of the CO₂-H₂ system were performed using an accurate intermolecular potential. These simulations provide theoretical predictions of H₂ broadening coefficients for CO₂ lines over a temperature range of 200–1000 K and for rotational quantum number up to J = 120. The predicted results show very good agreement with the experimental data, with difference of less than 3%, well below the precision required for exoplanet atmosphere studies. This work provides the first accurate and comprehensive dataset of H₂ broadening coefficients for CO₂ lines, suitable for modeling of H₂-rich exoplanetary atmospheres.