Recombination rate coefficients of Be-like neon

Abstract

Aims. Merged-beam and plasma recombination rate coefficients for Be-like Ne VII were extracted from results of a merged-beam type experiment.Methods. The cryring heavy-ion storage ring was used to determine merged-beam recombination rate coefficients for Be-like Ne6+. Recombined ions were separated from the stored beam in the first dipole magnet following the electron-ion interaction region. Field-ionization at this dipole magnet prevented detection of recombination into states with the principal quantum number n > n cutoff=23. To account for the field-ionization effects, results obtained with autostructure calculations were used for recombination channels above . The merged-beam recombination rate coefficients were then convoluted with Maxwellian electron energy distributions in the 103?3 × 106K temperature region, to obtain plasma recombination rate coefficients.Results. Good agreement was found between the experimentally derived rate coefficient spectrum and results of the autostructure calculation. At low energies, several strong dielectronic recombination resonances belonging to the spin-forbidden series dominate the merged-beam spectrum. Recombination through these states dominates at low-temperatures, e.g. at 103 K recombination through these resonances is more than one order of magnitude higher than the radiative recombination rate coefficient. Most data from the literature significantly underestimate the low-temperature plasma rate coefficients below 104 K, with only two calculations showing rate coefficients comparable to our results. Strong contributions from trielectronic recombination were found in the merged-beam spectrum of Be-like Ne, associated with double excitation of the Be-like Ne core, during the attachment of the free electron. Calculated trielectronic recombination resonance positions agree with experimental peaks, however compared to the experiment, the calculation underestimates the strength of trielectronic recombination.. © 2008 ESO.