Dielectronic recombination resonances in ${\mathrm{Na}}^{8+}$

The electron-ion recombination spectrum of the Li-like ${\mathrm{Na}}^{8+}$ ion in the energy range $0.0–0.5\mathrm{eV}$ is presented. Experimental results obtained by storage-ring techniques are compared with a calculated spectrum, based on a combination of relativistic many-body methods and complex rotation, and the agreement is found to be very good. The deviations between measured and calculated dielectronic recombination resonance energies are usually below about $2\mathrm{meV}$ with a maximum difference at $5.5\mathrm{meV}$, while the theoretical cross sections deviate by at most 20% from the experiment. The recombination spectrum in the investigated energy region is determined by the $2p_{j}7{\ell }_{j^{\prime }}$ Rydberg manifold of dielectronic recombination resonances, comprising 61 states within half an eV above the ground state of ${\mathrm{Na}}^{8+}$. The theoretical resonance parameters of all contributing states are provided.

Figure 1

(a) Comparison between theory (solid line) and experiment (data points) with no scaling between calculated and measured electron-ion recombination rate coefficients for ${\mathrm{Na}}^{8+}$. Resonances are labelled by their $jj$ configuration. For some resonances the dominating $LS$-term assignment is additionally given in boldface letters. The shaded spectrum is obtained by excluding resonances dominated by $LS$ terms that cannot autoionize. (b) Comparison between theory (thick solid line) and experiment (data points) on a logarithmic energy scale to emphasize the low-energy resonances. The dashed line shows the contribution from radiative recombination and the thin solid line that from dielectronic recombination alone.