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

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We study excitation and ionization in the 1.5 MeV/amu O⁸⁺-Li collision system, which was the subject of a recent reaction-microscope-type experiment [Fischer et al., Phys. Rev. Lett. 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.