Comprehensive Ab Initio Quantum Computations of CO ₂ –H ₂ and CO ₂ –He Collisional Properties

We present comprehensive ab initio fully quantum calculations of CO 2 –H 2 and CO 2 –He collisional properties. Our framework combines CCSD(T) potential-energy-surface calculations with close-coupling dynamical scattering in the Yumi framework to derive elastic and inelastic cross sections, rate coefficients, and pressure broadening parameters. We characterize the rotational dependence of the broadening coefficients up to j = 25 for CO 2 –H 2 and j = 40 for CO 2 –He, and their temperature dependence over 40–800 K. We also provide Padé fits as a function of rotational quantum number, enabling extrapolation and integration into spectroscopic databases, including HITRAN and HITEMP. The resulting pressure broadening coefficients reproduce available experimental measurements on an absolute scale, without empirical correction factors, and meet the ∼10% precision requirement identified for JWST-era exoplanet atmospheric studies. These calculations provide a substantial update to the pressure-broadening parameters commonly used in exoplanet atmospheric retrievals. The improvement is most important at elevated temperatures ( T ≥ 400 K), where existing database values such as those from HITRAN can fall outside the desired precision by up to a factor of five. All derivations, computed collisional properties, and database-ready products are provided with this manuscript. This methodology demonstrates the power of the next-generation quantum dynamics computations for spectroscopic needs across planetary atmospheres, combustion, health sciences, and fusion-plasma diagnostics.