Role of excitation inK-shell vacancy production forF6++He collisions

Cross sections have been measured for $K$-shell vacancy production for ${\mathrm{F}}^{6+}\left(1\mathrm{}{s}^{2}2s\right)$ ions incident on He target atoms in the projectile energy range from 10 to 40 MeV. Collisions leading to ${\mathrm{F}}^{6+}\mathrm{}\left(1s2s2p\right)\mathrm{}$ states are attributed to $K$-shell excitation. The cross sections for ${\mathrm{F}}^{6+}\left(1\mathrm{}{s}^{2}2s\right)$ to ${\mathrm{F}}^{6+}\mathrm{}\left(1s2s2p\right)\mathrm{}$ excitation agree with a Born calculation for $1s$-electron excitation. Collisions leading to ${\mathrm{F}}^{7+}\mathrm{}\left(1s2p\right)\mathrm{}$ states are referred to as $K$-vacancy production to distinguish it from the $K$-shell excitation process. The energy dependence of the $K$-vacancy production cross section for the ${\mathrm{F}}^{6+}\left(1\mathrm{}{s}^{2}2s\right)$ to ${\mathrm{F}}^{7+}\mathrm{}\left(1s2p\right)\mathrm{}$ process does not agree with the calculation for single $1s$-electron ionization. The observed energy dependence is understood in terms of the sum of two two-step processes. One two-step process is $1s$-electron ionization simultaneous with $2s-2p$-electron excitation and the other is $2s$-electron ionization simultaneous with $1s-2p$-electron excitation. The latter process is dominant. The ${\mathrm{F}}^{q+}$ charge-state dependence at 15 MeV and the ${\mathrm{F}}^{8+}$ energy dependence for electron excitation, as previously reported, are also compared with theory.