Present status of theoretical understanding of charge changing processes at low beam energies

TL;DR

This paper reviews the development and comparison of the ETACHA code models for predicting charge-state distributions of heavy ions in solid targets, highlighting the importance of non-perturbative processes and surface effects.

Contribution

It presents a detailed comparison of different ETACHA code versions and experimental data, emphasizing the role of nonradiative electron capture in charge state formation.

Findings

Earlier ETACHA versions predict charge states better for certain cases.

Non-perturbative processes significantly affect charge state predictions.

Surface electron capture influences multiply charge formation.

Abstract

A model for the evaluation of charge-state distributions of fast heavy ions in solid targets is being developed since late eighties in terms of ETACHA code. Time to time it is being updated to deal with more number of electrons and non-perturbative processes. The calculation approach of the recent one, which is formulated for handling the non-perturbative processes better, is different from the earlier ones. However, the experimental results for the projectiles up to 28 electrons can be compared with the predictions from any versions of ETACHA code. Though earlier versions are not meant for the non-perturbative cases, but the detail comparison suggests that predictions from an earlier version is somewhat superior to that of the recent version. However, certain difference up to 4 units of charge found between the earlier version and experimental results on the mean charge states and charge state distributions is attributed to nonradiative electron capture taking place at the exit surface in the influence of wake and dynamic screening effects. This can be a possible mechanism of multiply charge formation in the electrospray ionization of big molecules.