Journal
ASTROPHYSICAL JOURNAL
Volume 908, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4357/abcc64
Keywords
Interstellar atomic gas; Interstellar clouds; Interstellar medium; Interstellar absorption; Line intensities; Atomic spectroscopy; Line positions; X-ray astronomy; Laboratory astrophysics
Categories
Funding
- German Federal Ministry for Education and Research (BMBF) within the Verbundforschung funding scheme [05K16GUC, 05K16RG1, 05K16SJA]
- Initiative and Networking Fund of the Helmholtz Association through the Young Investigators Group program
- NASA Astrophysics Research and Analysis Program
- Astrophysics Data Analysis Program
- Alexander von Humboldt Foundation
- [SFB 755]
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Using the photon-ion merged-beams technique at a synchrotron light source, relative cross sections for single and up to five-fold photoionization of Fe2+ ions in the energy range of 690-920 eV were measured. Theoretical calculations showed good agreement with experimental data when energy shifts were applied and assumptions were made about the initial experimental population. Extensive calculations of Auger cascades from removing electrons from the 2p subshell of Fe2+ led to better agreement with the measured product-charge-state distributions.
Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe2+ ions in the energy range of 690-920 eV. This range contains thresholds and resonances associated with ionization and excitation of 2p and 2s electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5 eV are applied to the calculated resonance positions and assumptions are made about the initial experimental population of the various levels of the Fe2+([Ar]3d(6)) ground configuration. Furthermore, we performed extensive calculations of the Auger cascades that result when an electron is removed from the 2p subshell of Fe2+. These computations lead to a better agreement with the measured product-charge-state distributions as compared to earlier work. We conclude that the L-shell absorption features of low-charged iron ions are useful for identifying gas-phase iron in the interstellar medium and for discriminating against the various forms of condensed-phase iron bound to composite interstellar dust grains.
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