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Photoionization of metastable heliumlike C4+(1s2s S1 3) ions: Precision study of intermediate doubly excited states

  • Author(s): Müller, A
  • Lindroth, E
  • Bari, S
  • Borovik, A
  • Hillenbrand, PM
  • Holste, K
  • Indelicato, P
  • Kilcoyne, ALD
  • Klumpp, S
  • Martins, M
  • Viefhaus, J
  • Wilhelm, P
  • Schippers, S
  • et al.
Abstract

In a joint experimental and theoretical endeavor, photoionization of metastable C4+(1s2sS13) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s, and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25 800 which is sufficient to separate the leading fine-structure components of the 2s2pP3 term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. Their uncertainties are estimated to be below ±1 meV. Detailed balance confirms the present photoionization cross-section results by comparison with previous dielectronic-recombination measurements. The high accuracy of the theoretical transition energies together with the present experimental results qualify photoabsorption resonances in heliumlike ions as new, greatly improved energy-reference standards at synchrotron radiation facilities.

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