Role of two-electron processes in the excitation-ionization of lithium atoms by fast ion impact

TL;DR

This study investigates excitation and ionization in lithium atoms caused by fast ion impact, emphasizing the importance of two-electron processes and shake-off effects for accurately matching experimental data.

Contribution

It demonstrates that two-electron excitation-ionization processes are essential and introduces an independent-event model with shake-off to improve theoretical-experimental agreement.

Findings

Single ionization of lithium K-shell is insufficient to explain data.

Two-electron excitation-ionization processes are significant.

Including shake-off improves model accuracy.

Abstract

We study excitation and ionization in the 1.5 MeV/amu O$^{8+}$-Li collision system, which was the subject of a recent reaction-microscope-type experiment [Fischer \textit{et al.}, Phys. Rev. Lett. \textbf{109}, 113202 (2012)]. Starting from an independent-electron model based on determinantal wave functions and using single-electron basis generator method and continuum distorted-wave with eikonal initial-state calculations we show that pure single ionization of a lithium $K$-shell electron is too weak a process to explain the measured single differential cross section. Rather, our analysis suggests that two-electron excitation-ionization processes occur and have to be taken into account when comparing with the data. Good agreement is obtained only if we replace the independent-electron calculation by an independent-event model for one of the excitation-ionization processes and also take a shake-off process into account.