Single electron capture byHe+in Mg and Pb vapors

The single-electron capture cross section ${\sigma }_{10}$ for ${\mathrm{He}}^{+}$ ions on magnesium and lead vapors has been measured in the energy range 9-40 keV. The results are not in agreement with the conventional near-adiabatic criterion of Massey regarding the energy at which the cross sections ${\sigma }_{10}$ are maxima. This is thought to be due to pseudocrossing of potential-energy curves. Cross sections for Mg are found to be larger than for Pb in spite of the fact that both targets have very similar ionization potentials for their outer electrons.