| Themes > Science > Physics > Molecular Physics > Excitation Energy Transfer and Energy Migration > Resonances and negative ions > Electron-Ion Recombination |
The understanding of the electron-ion recombination process is important in astrophysical and fusion plasma. In dilute plasma the simple processes of radiative recombination and dielectronic recombination dominates (see the picture below for a schematic explanation). In both processes the excess energy and momenta of the recombining electron are carried away by a photon. Radiative recombination is the direct process while dielectronic recombination is a resonant process where an autoionizing state of the recombined ion is utilized as an intermediate stage towards recombination. The transition into the doubly excited state is radiationsless and at least one target electron is involved. Being in the excited state the system has an increased probability to emit a photon and after that recombination is completed. Electron-ion recombination is studied in storage rings where cold ions and electrons collide with a well defined relative energy and the recombination process can be followed in detail. The studies are done for ions of almost any degree of ionization. We work with calculations in close connection with experiments, especially at the CRYRING storage ring in Stockholm. Since it is necessary to describe doubly excited states in medium or highly charged ions where a relativistic treatment is essential we have developed a scheme based on relativistic many-body perturbation theory combined with the method of complex rotation. |
| Fig. Nearby charge-states can have enormously different probability to recombine with electrons due to the presence of resonances. Pb53+ recombines 100 times more efficient than Pb54+. As shown in the picture radiative recombination (RR) can explain the recombination rate in Pb54+. Dielectronic recombination (DR) resonances must be responsible for the enhanced rate in Pb53+, see the next slide for more explanations. |
| Fig. Pb53+
recombines into Pb52+ which has several resonances (due to the
presence of doubly excited states) just above its ionization threshold. In
the experiment the first resolved resonance can be seen around 3 mV above
the ionization threshold. Together with a calculation of the relative
resonance positions this can be used to fix the Pb53+(4p1/2-4s1/2)
energy difference to within 1 meV which is beyond the accuracy obtainable
with present methods for calculations of Quantum Electrodynamics in a
many-body system, see Prl 86, 5027. |
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