Electron capture by and electron excitation of two-electron fluorine ions incident on helium

It is demonstrated that the total F $K$ x-ray production cross section for ${\mathrm{F}}^{7+}$ + He collisions comes predominantly from three types of processes. These processes are $1s$-electron excitation of the $1s^2{}_{}{}^1{}_{}{}^{}S$ ground state of ${\mathrm{F}}^{7+}$, $2s$ electron excitation of the $1s2s{}_{}{}^3{}_{}{}^{}S$ metastable state of ${\mathrm{F}}^{7+}$, and $\mathrm{nl}$ electron capture by the $1s2s{}_{}{}^3{}_{}{}^{}S$ metastable state of ${\mathrm{F}}^{7+}$. All three of these processes have one thing in common, namely, they result in F $K$ x rays. By using a high-resolution x-ray spectrometer, the cross sections for the three processes are measured separately as a function of projectile energy in the range of 6 to 40 MeV. The assignment of the three different processes of $1s$ electron excitation, $2s$ electron excitation, and $\mathrm{nl}$ electron capture is corroborated by comparing the measured energy dependences of the various $K$ x-ray transitions with theory and other experimental measurements with ${\mathrm{F}}^{8+}$ and ${\mathrm{F}}^{9+}$ beams.