Photorecombination of ions: search for interference effects, recombination at low energies and rate coefficient in plasmas

Abstract

In the search for interference between radiative and dielectronic recombination (RR and DR), absolute recombination rate coefficients for Ar-like ions have been measured at the Heidelberg Test Storage Ring in the centre-of-mass energy range 0-80 eV. The dominant recombination channels beside RR is DR via the formation of (33d ) and (33d ) intermediate doubly excited states. The DR rate coefficient in plasmas is inferred from this measurement. It is about a factor of 3 lower than the previously available result based on a semi-empirical calculation. Asymmetric lineshapes due to quantum mechanical interference as recently predicted theoretically for isoelectronic ions have not been observed. The broad (3) DR resonance expected on the basis of multi-configuration Hartree-Fock calculations at 3.0 eV with a width of 1.3 eV appears to be shifted towards zero centre-of-mass energy where an unexplained recombination rate enhancement of a factor of 2 beyond the sum of RR and DR rates is observed.