Absolute cross-section measurements for electron-impact ionization of doubly charged ions ${\mathrm{Ti}}^{2+}$, ${\mathrm{Fe}}^{2+}$, ${\mathrm{Ar}}^{2+}$, ${\mathrm{Cl}}^{2+}$, and ${\mathrm{F}}^{2+}$

Measurements have been made of the cross section for electron-impact single ionization of the ions ${\mathrm{Ti}}^{2+}$, ${\mathrm{Fe}}^{2+}$, ${\mathrm{Ar}}^{2+}$, ${\mathrm{Cl}}^{2+}$, and ${\mathrm{F}}^{2+}$, spanning the range of energies from below threshold to 1500 eV. Indirect processes such as excitation-autoionization contribute substantially to the cross section for ${\mathrm{Ti}}^{2+}$, while such contributions are less pronounced for the other species. Comparisons with available theoretical predictions and with the Lotz semiempirical formula are presented. Expansion coefficients and formulas for generating ionization rate coefficients in the temperature range ${10}^4$<T${<10\mathrm{}}^7$ K are included for each ion.