# Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen

## TL;DR

This study calculates excitation and charge transfer rates in low-energy hydrogen collisions with neutral carbon and nitrogen, highlighting the significance of charge transfer processes in stellar atmosphere modeling.

## Contribution

It introduces a method combining LCAO and Landau-Zener models to compute collision rates for C I and N I, emphasizing the importance of charge transfer in non-LTE stellar spectra modeling.

## Key findings

- Charge transfer rates are larger than excitation rates.
- Two-electron processes can significantly impact statistical equilibrium.
- Approximate modeling of two-electron processes needs validation.

## Abstract

Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We have calculated and studied excitation and charge transfer of C i and of N i due to such collisions. We used a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau-Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes do, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.