Independent-particle and independent-event calculations for 1.5 MeV/amu O$^{8+}$-Li collisions

In a recent experiment, ionization in 1.5 MeV/amu O$^{8+}$-Li collisions was considered [1]. The measured spectra exhibit two distinct peaks, which were identified as being due to the removal of the $2s$- and the removal of one of the $1s$-electrons, respectively. Since a continuum-distorted wave with eikonal initial state (CDW-EIS) calculation for Li($1s$) ionization did not agree with the measured electron-energy differential cross section associated with the second peak, it was concluded that it may be due to a two-electron excitation-ionization process not accounted for in the calculation. In order to test this interpretation we have combined single-particle CDW-EIS calculations for ionization with basis generator method calculations for excitation using both independent-particle and independent-event models. We find that the proposed two-electron process, in which a $1s$ electron is promoted to an excited state while the $2s$ electron is ionized, does contribute, but cannot fully explain the experimental cross section. Rather, one has to consider the sum of various processes in which a vacancy is created in the Li $K$-shell to obtainaccebtable agreement with the data.\\[4pt] [1] D. Fischer {\it et al.}, Phys. Rev. Lett. \textbf{109}, 113202 (2012).