| Abstract
| - Aims. 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. Methods. 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. Results. 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.
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