Electron-impact ionization of multicharged metal ions: ${\mathrm{Ni}}^{3+}$, ${\mathrm{Cu}}^{2+}$, ${\mathrm{Cu}}^{3+}$, and ${\mathrm{Sb}}^{3+}$

Absolute electron-impact ionization cross sections were measured as a function of collision energy for the multicharged metallic ions ${\mathrm{Ni}}^{3+}$, ${\mathrm{Cu}}^{2+}$, ${\mathrm{Cu}}^{3+}$, and ${\mathrm{Sb}}^{3+}$. The measurements cover an energy range from below threshold to 1000 eV (1500 eV for ${\mathrm{Cu}}^{2+}$). Recent distorted-wave direct ionization calculations agree with the measurements for ${\mathrm{Ni}}^{3+}$, ${\mathrm{Cu}}^{2+}$, and ${\mathrm{Cu}}^{3+}$ within 20%. Inner-shell excitation followed by autoionization produces up to a factor-of-2 enhancement in the ${\mathrm{Sb}}^{3+}$ cross section, and a rapid decrease in this indirect contribution at higher energies indicates the dominance of dipole-forbidden excitations.