Population of Atomic Levels by Dielectronic Recombination.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Population of Atomic Levels by Dielectronic Recombination. Goldberg, Leo ; Dupree, Andrea K. Abstract Under conditions found in H II regions, the populations of excited levels of atoms are determined primarily by the balance between electronic recombination and cascade into the levels and spontaneous transitions out of them. The bare nucleus of a hydrogenic ion can combine only by radiative capture but an ion that has one or more electrons can capture an electron by dielectronic recombination. This process may occur at a much faster rate and with a wholly different dependence on n and 1 than that of radiative capture. Illustrative calculations have been performed for Ca I in which the levels are assumed to be populated by dielectronic and three-body recombination and cascade, and to be depopulated by spontaneous downward transitions and collisional ionization. The results show that (1) the capture of electrons by dielectronic recombination can greatly increase the populations of highly excited levels as compared with their equilibrium values; (2) there will be a value of the total quantum number n for which bn, the ratio of the actual population to that in thermodynamic equilibrium, has a maximum value. This maximum occurs at n~50 to 100 for Ne=104 cm-3 and at n~100 to 200 for Ne=102 cm-3 (3) recombination lines from complex atoms should be found in emission and, with the appropriate conditions, in absorption. Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110439 Bibcode: 1967AJ.....72Q.799G full text sources ADS |