Rovibrational cross sections for the CO2 0000, 0110, 0220, and Fermi resonance states 1000(1) and 1000(2) in collisions with He atoms

We present quantum scattering calculations of CO2–He state-to-state integral cross sections for 25 transition sets, covering pure rotational transitions within and rovibrational transitions between: the ground state 0000, the bend fundamental 0110, the bending overtone 0220, and the Fermi doublet states 1000(1) and 1000(2). Exact coupled-channel (CC) and coupled-states approximation (CSA) calculations are performed using a new five-dimensional potential energy surface. The calculations cover collision energies from 20 to 5220 cm−1, sufficient to obtain converged rate coefficients over 100–800 K, and include initial rotational states for each transition up to at least j = 35. We present an energy-grid algorithm for rovibrational quantum scattering calculations that minimizes the number of separate calculations required. The resulting cross sections exhibit a dominant Δj = 0 propensity and parity-dependent patterns. For the benchmark 0000, j′ ← 0110, j transition, thermally averaged rate coefficients reproduce available experimental data. A comparison between the CC and CSA cross sections shows that for vibrational quenching transitions, the CSA cross sections increasingly deviate from the CC results with increasing initial rotational state j. Calculated integral cross sections cover collision energies and rotational states needed to derive rate coefficients for radiative transfer modeling of mid-infrared CO2 spectra from environments that are not in local thermal equilibrium. The computationally simpler CO2–He system allows the methodology and approximations to be tested at high collision energies and rotational states, helping assess their suitability for the more complex and astrochemically important CO2–H2 system.