2016A&A...587A.114B

Inelastic processes in low-energy Ca + H and Ca⁺ + H^– collisions are treated for the states from the ground state up to the ionic state with the aim to provide rate coefficients needed for non-LTE modeling of Ca in cool stellar atmospheres. The electronic molecular structure was determined using a recently proposed model approach that is based on an asymptotic method. Nonadiabatic nuclear dynamics were treated by means of multichannel formulas, based on the Landau-Zener model for nonadiabatic transition probabilities. The cross sections and rate coefficients for inelastic processes in Ca + H and Ca⁺ + H^– collisions were calculated for all transitions between 17 low-lying covalent states plus the ionic state. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Ca(4s5s ^1,3S) and the ionic Ca⁺ + H^– states. The next group with the second highest rate coefficients includes the processes involving the Ca(4s5p ^1,3P), Ca(4s4d ^1,3D), and Ca(4s4p ¹P) states. The processes from these two groups are likely to be important for non-LTE modeling.