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

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 induced pressure-broadening and pressure-shift coefficients were determined at room temperature for the entire nu3 band of CO2 in the 4.3 micrometer 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.