Measurement of the contribution of excitation autoionization to electron-impact ionization of ions:Ti3+,Zr3+,Hf3+, andTa3+

Measurements were made of the cross section for electron-impact single ionization of the transition-element ions ${\mathrm{Ti}}^{3+}$, ${\mathrm{Zr}}^{3+}$, ${\mathrm{Hf}}^{3+}$, and ${\mathrm{Ta}}^{3+}$ for an electron-energy range from threshold to 1000 eV. The cross sections are enhanced by as much as a factor of 20 due to excitation autoionization primarily involving $\Delta n=0\mathrm{}$ transitions, $n{p}^{6}n{d}^m\to n{p}^{5}n{d}^{m+1\mathrm{}}$. Comparisons with recent theoretical predictions show reasonable agreement between measured and predicted positions of the autoionization states; however, the magnitudes of the theoretical cross sections are greater than the experimental values by a factor of approximately 2.5.