Excitation-ionization of lithium atoms by fast ion impact: the independent-electron model and beyond

We report on a theoretical study of one-electron and two-electron processes in the ion-impact-induced ionization of lithium atoms [1]. An independent-electron model (IEM) description based on basis-generator-method and continuum-distorted-wave-eikonal-initial-state single-particle probabilities is applied to calculate $1s$ and $2s$ vacancy production single-differential cross sections, which were measured with the recently developed MOTReMi apparatus [2]. We find that the IEM predicts a considerable role of two-electron excitation-ionization processes in $1s$-vacancy production, but is not sufficient to explain the data. Replacing the IEM by an independent-event model for one of the contributing excitation-ionization processes and also taking a shake-off process into account improves the comparison with the measurements significantly. \\[4pt] [1] T. Kirchner {\it et al.}, Phys. Rev. A {\bf 89}, 062702 (2014).\\[0pt] [2] D. Fischer {\it et al.}, Phys. Rev. Lett. {\bf 109}, 113202 (2012).