Atomic data on inelastic processes in low-energy manganese-hydrogen collisions ^⋆

¹ Max-Planck Institute for Astrophysics, Postfach 1371, 85741 Garching, Germany
e-mail: andrey.k.belyaev@gmail.com
² Department of Theoretical Physics and Astronomy, Herzen University, 191186 St. Petersburg, Russia

Received: 31 May 2017
Accepted: 3 July 2017

Abstract

Aims. The aim of this paper is to calculate cross sections and rate coefficients for inelastic processes in low-energy Mn + H and Mn⁺ + H⁻ collisions, especially, for processes with high and moderate rate coefficients. These processes are required for non-local thermodynamic equilibrium (non-LTE) modeling of manganese spectra in cool stellar atmospheres, and in particular, for metal-poor stars.

Methods. The calculations of the cross sections and the rate coefficients were performed by means of the quantum model approach within the framework of the Born-Oppenheimer formalism, that is, the asymptotic semi-empirical method for the electronic MnH molecular structure calculation followed by the nonadiabatic nuclear dynamical calculation by means of the multichannel analytic formulas.

Results. The cross sections and the rate coefficients for low-energy inelastic processes in manganese-hydrogen collisions are calculated for all transitions between 21 low-lying covalent states and one ionic state. We show that the highest values of the cross sections and the rate coefficients correspond to the mutual neutralization processes into the final atomic states Mn(3d⁵4s(⁷S)5s e ⁶S), Mn(3d⁵4s(⁷S)5p y ⁸P°), Mn(3d⁵4s(⁷S)5s e ⁸S), Mn(3d⁵4s(⁷S)4d e ⁸D) [the first group], the processes with the rate coefficients (at temperature T = 6000 K) of the values 4.38 × 10^-8, 2.72 × 10^-8, 1.98 × 10^-8, and 1.59 × 10^-8 cm³/ s, respectively, that is, with the rate coefficients exceeding 10^-8 cm³/ s. The processes with moderate rate coefficients, that is, with values between 10^-10 and 10^-8 cm³/ s include many excitation, de-excitation, mutual neutralization and ion-pair formation processes. In addition to other processes involving the atomic states from the first group, the processes from the second group include those involving the following atomic states: Mn(3d⁵(⁶S)4s4p (¹P°) y ⁶P°), Mn(3d⁵4s(⁷S)4d e ⁶D), Mn(3d⁵4s(⁷S)5p w ⁶P°), Mn(3d⁵(⁴P)4s4p (³P°) y ⁶D°), Mn(3d⁵(⁴G)4s4p (³P°) y ⁶F°). The processes with the highest and moderate rate coefficients are expected to be important for non-LTE modeling of manganese spectra in stellar atmospheres.