Dielectronic recombination of iron L-shell ions

An experimental program to study low temperature dielectronic recombination (DR) in the iron L-shell ions Fe17+ to Fe23+ is currently in progress at the TSR heavy-ion storage ring in Heidelberg, Germany. L-shell iron ions play an important role in determining the line emission and thermal and ionization structures of cosmic photoionized plasmas. Successful modelling of these plasmas requires accurate ionization and recombination rates, particularly for low temperature DR which is the dominant recombination mechanism for most iron ions in photoionized plasmas. The dependence of DR on the detailed atomic structure makes it challenging to determine the needed DR rate coefficients theoretically, especially in many-electron systems. Our systematic survey of Li- to F-like Fe-ions is designed to produce high-resolution DR spectra which can be used to benchmark theory for ions of increasing complexity and to provide absolute low-temperature DR rates required in astrophysics. (orig.)