Observation of Two-Electron Penning Ionization in a Thermal-Energy Collision

Abstract

The existence of the hybrid Penning reaction, ${\mathrm{He}}^{+}+X\to \mathrm{He}+X^{++}+e$, has been confirmed for thermal-energy collisions of ${\mathrm{He}}^{+}$ with Mg, Ca, Sr, Ba, Y, Ce, Yb, Sn, and Pb. A new two-electron Penning reaction, ${\mathrm{He}}^{*}+X\to \mathrm{He}+X^{++}+2e$, has been identified in $\mathrm{H}\mathrm{e}*$-Ce and $\mathrm{H}\mathrm{e}*$-Y collisions.