Near L-Edge Single and Multiple Photoionization of Singly Charged Iron Ions

Abstract

Absolute cross sections for m-fold photoionization (m=1,...,6) of Fe+ by a single photon were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source, operated by DESY in Hamburg, Germany. Photon energies were in the range 680-920 eV which covers the photoionization resonances associated with 2p and 2s excitation to higher atomic shells as well as the thresholds for 2p and 2s ionization. The corresponding resonance positions were measured with an uncertainty of +- 0.2 eV. The cross section for Fe+ photoabsorption is derived as the sum of the individually measured cross-sections for m-fold ionization. Calculations of the Fe+ absorption cross sections have been carried out using two different theoretical approaches, Hartree-Fock including relativistic extensions and fully relativistic Multi-Configuration Dirac Fock. Apart from overall energy shifts of up to about 3 eV, the theoretical cross sections are in good agreement with each other and with the experimental results. In addition, the complex deexcitation cascades after the creation of inner-shell holes in the Fe+ ion have been tracked on the atomic fine-structure level. The corresponding theoretical results for the product charge-state distributions are in much better agreement with the experimental data than previously published configuration-average results. The present experimental and theoretical results are valuable for opacity calculations and are expected to pave the way to a more accurate determination of the iron abundance in the interstellar medium.

18 pages, 10 figures, 4 tables, accepted for publication in The Astrophysical Journal

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• The photon-ion merged-beams experiment PIPE at PETRAIII - The first five years
• Near L-Edge Single and Multiple Photoionization of Doubly Charged Iron Ions
• Near--K-edge double and triple detachment of the F- negative ion: observation of direct two-electron ejection by a single photon
• Photoionization of astrophysically relevant atomic ions at PIPE
• Multiple photodetachment of atomic anions via single and double core-hole creation
• High-Resolution X-Ray Spectroscopy of Interstellar Iron Toward Cygnus X-1 and GX 339-4
• Near K-Edge Photoionization and Photoabsorption of Singly, Doubly, and Triply Charged Silicon Ions