Electron capture by metastable projectiles on He and Ne

Abstract

Electron capture to $n\ge 2$ levels of ${\mathrm{F}}^{7+}$ $\left(1s2s\right){}_{}{}^3{}_{}{}^{}S$ projectiles lead to three-electron ions with an energetically allowed $K$-Auger decay channel. We have measured the F $K$-Auger emission spectra for collisions with thin gas targets of He and Ne with sufficiently high resolution to distinguish capture to several of the low-lying $n$ values. The $K$-Auger production cross sections are reported as a function of the $n$ level into which the electron is captured. The $n$-level dependence is measured for projectile energies of 6, 9, 12, and 15 MeV and is compared to the Oppenheimer-Brinkman-Kramers OBK model for charge transfer and to a $\frac{1}{n^3}$ function. The measured $K$-Auger electron-production cross sections closely follow the $\frac{1}{n^3}$ function which differs from the predicted OBK $n$ dependence, even though the cross sections for the higher $n$ levels agree with the predicted OBK energy dependence. The effects of cascading upon the calculated $n$ dependence are also studied.