Dielectronic Recombination of Iron M-shell Ions: Fe ⁶⁺ –Fe ³⁺ *

Dielectronic recombination (DR) rate coefficients of Fe 6+ –Fe 3+ ions are calculated using the multiconfiguration Breit–Pauli approach as implemented in the autostructure code. A large-scale electron correlation between n = 3 and n = 4 configurations is considered in the present calculations, and semiempirical corrections to the near-threshold resonance energies are also applied, to improve the results at low temperatures. The present DR rate coefficients are greater than those previously calculated and currently used by CLOUDY, ION, and XSTAR by up to an order of magnitude. These DR rate coefficients of Fe 6+ –Fe 3+ , along with our previous results for Fe 8+ and Fe 7+ , are crucial for accurately determining the ionization balance of M-shell iron ions. The present increased DR rate coefficients would shift the predicted ionization equilibrium of these ions towards lower charge states.