Contributions of dielectronic, trielectronic, and metastable channels to the resonant intershell recombination of highly charged silicon ions

Intershell, resonant electronic recombination is studied experimentally in an electron-beam ion trap for O-like ${\mathrm{Si}}^{6+}$ to He-like ${\mathrm{Si}}^{12+}$ ions at plasma temperatures in the megakelvin range similar to those found in the solar radiative zone and is compared to extended multiconfiguration Dirac-Fock and relativistic configuration-interaction predictions. For this low-$Z$ ion, the higher-order electronic recombination processes are comparable in strength to the first-order one. The ratio of trielectronic to dielectric recombination for B-like species agrees well with predictions, whereas for C-like ions the measured value is only half as large. This difference is explained by the influence of metastable states populated in the recombining plasma.