Inelastic silicon-hydrogen collision data for non-LTE applications in stellar atmospheres^⋆

¹ Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
e-mail: andrey.k.belyaev@gmail.com
² Department of Theoretical Physics and Astronomy, Herzen University, 191186 St. Petersburg, Russia

Received: 30 July 2014
Accepted: 17 September 2014

Abstract

Aims. Inelastic processes in low-energy Si + H and Si⁺ + H⁻ collisions are treated for the states from the ground state up to the ionic state, in order to provide rate coefficients needed for non-LTE modeling of Si in cool stellar atmospheres.

Methods. Electronic molecular structure is determined using a recently proposed model approach based on an asymptotic method in combination with available ab initio potentials. Nonadiabatic nuclear dynamics are treated by means of a combination of multichannel formulas and the branching-probability-current method, based on the Landau-Zener model for nonadiabatic transition probabilities.

Results. Cross sections and rate coefficients for inelastic processes in Si + H and Si⁺ + H⁻ collisions for all transitions between 26 low-lying states plus the ionic state are calculated. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Si(3p4p ³D), Si(3p3d ³F), Si(3p4p ¹D), Si(3p3d ³P), Si(3p4p ¹S), and the ionic Si⁺ + H⁻ states. These processes are likely to be important in non-LTE modeling.