Measurements and predictions of H ₂ pressure-broadening coefficients of CO ₂ absorption lines for exoplanet atmosphere studies

Accurate and comprehensive H 2 pressure-induced broadening data for CO 2 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, H 2 pressure-induced broadening and pressure-shift coefficients were determined at room temperature for the entire ν 3 band of CO 2 in the 4.3 µm spectral region using a high-resolution Fourier transform spectrometer. In addition, requantized molecular dynamics simulations of the CO 2 -H 2 system were performed using an accurate intermolecular potential. These simulations provide theoretical predictions of H 2 broadening coefficients for CO 2 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 H 2 broadening coefficients for CO 2 lines, suitable for modeling of H 2 -rich exoplanetary atmospheres.