Nickel-like ions have a metastable level (${3d}^{9}4s {{}^{3}D}_3$) that decays exclusively by a magnetic octupole ($M3$) transition. We earlier have measured the lifetime of this level in isotopically pure Ni-like Xe ions and have shown how hyperfine interaction modifies the lifetime. We now demonstrate how this long-lived level enables multistep ionization of Ni-like ions at much lower energies than the usual single-step ionization limit, even at the relatively low densities of our electron beam ion trap. Time-resolved and energy-varying observations of ${\mathrm{Xe}}^{26+}$ (Ni-like) and ${\mathrm{Xe}}^{27+}$ (Co-like) in an electron beam ion trap indicate the notable influence of the metastable level on the charge balance in a plasma. The interpretation of our observations is helped by collisional-radiative modeling with hybrid models based on the Flexible Atomic Code, which furthermore enables quantification.

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• Electronic excitation & ionization
• Electronic structure of atoms & molecules