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

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 induced pressure-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.