Electron-impact ionization ofB2+andO5+: Excitation-autoionization in Li-like ions

New measurements for the total, single ionization of ${\mathrm{B}}^{2+}$ and ${\mathrm{O}}^{5+}$ by electron impact are reported with particular attention directed to the indirect contribution of excitation-autoionization. For ${\mathrm{B}}^{2+}$ these are the first measurements to our knowledge while for ${\mathrm{O}}^{5+}$ the present data improve on previous measurements. In both cases the direct total ionization cross sections are in good agreement with recent distorted-wave predictions of Younger, and the excitation-autoionization contribution is consistent with measurements for other Li-like ions. For ${\mathrm{O}}^{5+}$ an additional small increase in the cross section is observed at an energy well below the excitation-autoionization threshold; this feature may be attributable to resonance recombination followed by auto-double-ionization. For the Li-like ions ${\mathrm{Be}}^{+}$, ${\mathrm{B}}^{2+}$, ${\mathrm{C}}^{3+}$, ${\mathrm{N}}^{4+}$, and ${\mathrm{O}}^{5+}$, the ionization theory of Younger is used as a basis to subtract the direct ionization component from the total measured ionization cross sections in order to extract the 1$s^2$2s→${\mathcal{J}}_l$1s2s2l excitation cross section. The deduced inner-electron excitation cross sections are quantitatively compared with excitation theory including new close-coupling calculations for ${\mathrm{Be}}^{+}$ and ${\mathrm{B}}^{2+}$ presented here. For all cases except ${\mathrm{Be}}^{+}$, the close-coupling theory is in agreement with the deduced experimental excitation cross sections. These new results and analysis improve confidence in excitation theory for highly charged ions.