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51+ ions has been studied at the TSR. With Au 50+ ions a storage lifetime of only 2 to 4 s was observed with the magnetically expanded electron beam of the cooler at a density of ne = 10 7 cm −3. This short storage time is a consequence of the highest recombination rate coefficient ever observed with an atomic ion (1.8 · 10 −6 cm 3 s −1 at zero relative(More)
We present experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W 18+ ([Kr] 4d 10 4f 10) forming W 17+. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping recombination resonances. In the temperature range where the fractional abundance(More)
Recent observations of H 2 and H + 3 in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H + 3 and H 2 should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H + 3 /H 2 collision system at low(More)
The iron L-shell ions (Fe 17+ to Fe 23+) play an important role in determining the thermal and ionization structures and line emission from photoionized plasmas. Current uncertainties in the theoretical low temperature dielectronic recombination (DR) rate coefficients for these ions significantly affect our ability to model and interpret the line emission(More)
An introduction to electron}ion recombination processes is given and recent measurements are described as examples, focusing on low collision energies. Discussed in particular are "ne-structure-mediated dielectronic recombination of #uorine-like ions, the moderate recombination enhancement by factors of typically 1.5}4 found for most ion species at relative(More)
The low energy C IV dielectronic recombination (DR) rate coefficient associated with 2s→2p ∆n = 0 excitations of this lithiumlike ion has been measured with high energy-resolution at the heavy-ion storage-ring tsr of the Max-Planck-Institut für Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detection(More)
We have carried out direct measurements of the absolute recombination rate coefficients of four charge states of tungsten in the range from W 18+ to W 21+ in a heavy ion storage ring. We find that the rich atomic fine structure of the open f-shell leads to very high resonant enhancement of the recombination rate at energies below ∼50 eV. Even in the higher(More)
In recent years resonance reaction spectroscopy (RRS) by means of dielectronic recombination (DR) has been developed into a versatile tool for precision spectroscopy. At the electron cooler of the ESR, three major lines of RRS experiments are presently being pursued: (a) DR measurements with a stochastically (pre-) cooled beam, (b) DR isotope shift (IS)(More)
Spectroscopic results obtained on multiply charged few-electron ions by using laser-stimulated two-step recombination in ion storage rings are presented in an overview. Line splittings in transitions between Rydberg levels were observed for helium-like and beryllium-like ions. Emphasis is given to results on the beryllium-like system N 3+ where information(More)