Cross sections for electron-impact single ionization ofKr8+andXe8+

Absolute cross sections for electron-impact single ionization of ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ions were measured for energies below the ionization thresholds to 1500 eV using the crossed-beams method. A significant fraction of the ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ion beams were in metastable configurations. Configuration-average distorted-wave calculations for ions in the ground and first-excited configurations are compared to the experimental data. For both ions in this study, the excitation-autoionization contribution to the total ionization cross section is found to be much larger for ions in the first-excited configuration, which includes metastable levels, than for the ground-state ions. Maxwellian rate coefficients were calculated for ${\mathrm{Kr}}^{8+}$ and are compared to published results.