One-photon double ionization of helium: a heuristic formula for the cross section

TL;DR

This paper introduces a heuristic formula for calculating the cross sections in one-photon double ionization of helium, validated against experimental and ab initio data, and extends it to other ions.

Contribution

It presents a new heuristic formula for ionization cross sections that is benchmarked against experimental data and extended to other elements in the helium isoelectronic sequence.

Findings

The formula accurately reproduces helium's total ionization cross section.

It aligns well with ab initio calculations for Li+ ionization.

The framework is applicable to lithium and beryllium ionizations.

Abstract

Without a formal derivation, we propose a formula for the total and single-differential cross in the problem of one-photon double ionization of an atom. The formula is benchmarked against accurate experimental data for the total cross section of helium. Furthermore, a direct comparison with ab initio calculations for the double ionization of Li+ suggests that the framework is valid for the entire helium isoelectronic sequence. To this end, we introduce a formula for the double ionization of lithium, as well as for the triple ionization of lithium and beryllium.