Electron-impact excitation-autoionization in the cadmium isoelectronic sequence: A case of target term dependence in scattering theory

Excitation-autoionization contributions to electron-impact ionization are calculated for several atomic ions in the cadmium isoelectronic sequence. We calculate excitation cross sections in the distorted-wave approximation and compare them in one case to a calculation in the close-coupling approximation. We focus attention on the $4d^{10}5s^2\to 4d^{9}5s^2\mathrm{nf}$ innershell excitations in ${\mathrm{In}}^{+}$, ${\mathrm{Sb}}^{3+}$, and ${\mathrm{Xe}}^{6+}$. Hartree-Fock atomic structure calculations for the $4d^{9}5s^2\mathrm{nf}$ configurations are found to be highly term dependent. Thus our predictions for the total ionization cross section from the $5s$ subshell for these ions exhibit strong target term dependence. Our ${\mathrm{Xe}}^{6+}$ results are found to be in excellent agreement with the recent experimental crossed-beam measurements of Gregory and Crandall.