Comprehensive {Ab Initio}~Calculations of {CO2-H2} and {CO2-He} Collisional Properties

We present comprehensive {ab initio} calculations of CO₂-H₂ and CO₂-He collisional properties from first principles, employing CCSD(T), potential calculations together with close-coupling dynamical scattering in the ~framework. We derive (in)elastic cross sections, rate coefficients, and pressure-broadening parameters -- incl., their rotational dependence up to $|m|=50$, and temperature dependence over the range of 100-800 K. We provide Padé fits for the broadening coefficients as a function of rotational quantum number, enabling extrapolation of the results and integration into spectroscopic databases, including HITRAN and HITEMP. The computed potentials for both CO₂-H₂ and CO₂-He have a sub-percent precision, and the dynamics-solving code YUMI ultimately yields the collisional parameters. Among these, the scaled pressure broadening experimental values meet the 10% precision requirement for exoplanetary sciences with JWST. This contrasts with the parameters available before the present calculations, which at higher temperatures (T$>$400 K) deviate as much as 5× from the desired precision requirement. All derivations and collisional properties are provided with this manuscript, establishing the first of such a comprehensive ab initio foundation for collisional systems with a target molecule having more than two atoms.