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

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, deexcitation, ion-pair formation, and mutual neutralization processes involving the Si(3p4p 3 D), Si(3p3d 3 F), Si(3p4p 1 D), Si(3p3d 3 P), Si(3p4p 1 S), and the ionic Si + + H − states. These processes are likely to be important in non-LTE modeling.

Mg line formation in late-type stellar atmospheres

“…We wish to emphasize that with regard to hydrogen collisions in general, the accurate quantum (Barklem et al 2003;Barklem et al 2010Barklem et al , 2012 as well as the more approximate model calculations (Belyaev 2013;Belyaev et al 2014), based on a correct physical background, provide non-zero rate coefficients for both optically allowed and optically forbidden transitions, as well as for charge transfer processes, which generally have the highest rate coefficients among all hydrogen collision processes. Thus, the Drawin formula fails to provide reliable estimates for important inelastic processes in collisions with hydrogen.…”

Atomic data on inelastic processes in low-energy beryllium-hydrogen collisions

“…The present study of inelastic processes in beryllium-hydrogen collisions is performed by means of the quantum model approach within the framework of the Born-Oppenheimer formalism (Belyaev 2013a;Belyaev et al 2014b). The approach is based on the asymptotic method for calculations of adiabatic potentials and on the multichannel Landau-Zener model for computing inelastic transition probabilities.…”

“…Cross sections and rate coefficients for endothermic processes are calculated using the detailed balance equations (see, e.g., Belyaev et al 2014b). …”

“…The Drawin formula widely used in the past is not reliable at all (Barklem et al 2011), so other approximate but reliable approaches should be used. Approximate and physically reliable approaches to treat inelastic collisions of atoms and positive ions of different chemical elements with hydrogen atoms and negative ions have recently been proposed by Belyaev (2013a), Belyaev et al (2014b) within the framework of the Born-Oppenheimer approach. Since the treated inelastic processes are determined by nonadiabatic transitions, which are quantum by nature, the model approaches are essentially quantum as well.…”

“…Since the treated inelastic processes are determined by nonadiabatic transitions, which are quantum by nature, the model approaches are essentially quantum as well. These approaches have been applied to study aluminium (Belyaev 2013b), cesium (Belyaev et al 2014a), silicon (Belyaev et al 2014b), and calcium (Belyaev et al 2016) collisions with hydrogen. The main goal of these approaches is to calculate inelastic rate coefficients with high and moderate values, that is, rates of astrophysical interest, as well as estimate rate coefficients with low values, which are likely to be unimportant.…”