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 induced pressure-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.