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The influence of long-lived metastable levels on the electron-impact single ionization of C2+
Stockholm University, Faculty of Science, Department of Physics.
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2005 (English)In: Physical Review A, Vol. 71, no 1Article in journal (Refereed) Published
Abstract [en]

A joint theoretical and experimental investigation is made of the influence of long-lived metastable levels on the electron-impact single ionization of C2+. It is expected that our electron cyclotron resonance ion source produces a beam with 40% of the C2+ ions in the 1s22s2 1S0 ground level and 60% in the 1s22s2p  3P0,2 excited levels. The comparison of nonperturbative close-coupling calculations with previous single-pass crossed beams and with our multiple-pass storage-ring measurements for the electron-impact ionization of C2+ is consistent with the predicted large metastable fraction. Reasonable agreement is found between the present time-dependent close-coupling, R-matrix with pseudostates, and converged-close-coupling ionization cross-section calculations for the ground and first excited configuration, and experimental measurement, assuming a 60% metastable fraction in the ion beam. Distorted-wave calculations are found to overestimate the ionization cross section from both the ground and metastable terms, compared with nonperturbative calculations, resulting in an overestimation of the resultant total cross section when compared with experiment. It is clear that collisional-radiative modeling of the evolution of atomic plasmas through the Be-like ionization stage will need to take into account the role of both ground and metastable levels.

Place, publisher, year, edition, pages
2005. Vol. 71, no 1
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-25863DOI: 10.1103/PhysRevA.71.012716OAI: oai:DiVA.org:su-25863DiVA: diva2:200703
Note
Part of urn:nbn:se:su:diva-95Available from: 2004-04-05 Created: 2004-04-05 Last updated: 2010-08-09Bibliographically approved
In thesis
1. Recombination and ionization of astrophysically abundant ions
Open this publication in new window or tab >>Recombination and ionization of astrophysically abundant ions
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electron-ion recombination and electron-impact ionization of several astrophysically abundant C, N, O, and Ni ions have been investigated using the synchrotron storage ring CRYRING. The recombination rate coefficients predominanty used in the analyses of emission line spectra and for ionization balance calculations are determined from isoelectronic fits and extrapolations of theoretical and limited experimental results available from the literature. The rate coefficients reported by various authors differ by an order of magnitude for various ion species. For low temperature plasmas(<104 K), the available information on resonant recombination rate coefficients is even more limitied and, unfortunately, most available data has been determined from LS coupling calculations, which can have adverse effects on recombination rates due to the mistreatment of autoionizing states.

For ions of C, N, and O, the production of metastable states complicates the experimental rate coefficient determinations. Some attempts have been made in this work to utilize both recombination and electron-impact ionization in estimating the metastable ion beam fractions present. Other metastable fractions have been determined by comparing the experimental recombination spectra to intermediate coupling calculations. Some of the absolute recombination rate coefficients reported in this work are given for the first time while many others vastly improve the spectral resolution of previous experiments, allowing for a more detailed study of the low energy resonances which contribute to the resonant recombination rate coefficient at low plasma electron temperatures. This increased resolution has also lead to the observation of trielectronic recombination resonances which greatly influence low temperature recombinaion rates in some ions.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2004. 60 p.
Keyword
atomic data, plasma
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-95 (URN)91-7265-839-8 (ISBN)
Public defence
2004-04-26, sal FD5, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Available from: 2004-04-05 Created: 2004-04-05Bibliographically approved

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