Electron-impact ionization in the xenon isonuclear sequence

The distorted-wave approximation and electron-ion crossed beams have been employed to complete a theoretical and experimental study of electron-impact ionization along the Xe isonuclear sequence. Experimental results are given for ${\mathrm{Xe}}^{2+}$ through ${\mathrm{Xe}}^{6+}$ and the results of theoretical calculations are presented for ${\mathrm{Xe}}^{+}$ through ${\mathrm{Xe}}^{6+}$. The data reveal large contributions due to indirect ionization processes. Theoretical cross sections include the contributions of inner-shell excitations to autoionizing levels of the types ${\mathrm{Xe}}^{q+}\left({4d}^{10}{5s}^2{5p}^{6-q}\right)\to {\mathrm{Xe}}^{q+}\left({4d}^9{5s}^2{5p}^{7-q}\right)$ and ${\mathrm{Xe}}^{q+}\left({4d}^{10}{5s}^2{5p}^{6-q}\right)\to {\mathrm{Xe}}^{q+}\left({4d}^9{5s}^2{5p}^{6-q}nl\right)$ with $nl=4f,5d,\mathrm{and} 5f$. Hartree-Fock structure calculations for the ${4d}^9{5s}^2{5p}^{6-q}\mathrm{nf}$ configurations are highly term dependent and this has a pronounced effect on the magnitude and energy dependence of indirect contributions to the cross sections. Model calculations indicate that resonant-recombination double autoionization also contributes to the ionization cross sections of ${\mathrm{Xe}}^{2+}$ through ${\mathrm{Xe}}^{5+}$.