Excitation and charge transfer in low-energy hydrogen atom collisions with neutral atoms: Theory, comparisons, and application to Ca

TL;DR

This paper introduces a theoretical approach for estimating excitation and charge transfer cross sections in low-energy hydrogen atom collisions with neutral atoms, using an asymptotic two-electron model and the Landau-Zener framework, with applications to calcium.

Contribution

It presents a new asymptotic two-electron model method for calculating collision cross sections, validated against quantum calculations and applied to astrophysically relevant calcium-hydrogen interactions.

Findings

The method yields results consistent with full quantum calculations.

It provides rate coefficients for Ca+H collisions across 1000-20000 K.

The approach simplifies calculations using known atomic parameters.

Abstract

A theoretical method for the estimation of cross sections and rates for excitation and charge transfer processes in low-energy hydrogen atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen atom system, is presented. The calculation of potentials and non-adiabatic radial couplings using the method is demonstrated. The potentials are used together with the multi-channel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wavefunctions, which can be determined from known atomic parameters. The method is applied to Li+H, Na+H, and Mg+H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca+H collisions, and rate coefficients are calculated for temperatures in the range 1000-20000 K.