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  Cornetta, L. M.; Kjellsson, L.; Couto, R. C.; Ågren, H.; Carravetta, V.; Sörensen, S. R.; Kubin, M.; Bülow, C.; Zamudio-Bayer, V.; Issendorff, B. von; Lau, J. T.; Söderström, J.; Agåker, M.; Rubensson, J.-E.; Lindblad, R.: X-ray absorption spectrum of O₂⁺. Physical Review A 111 (2025), p. 022808/1-8

10.1103/PhysRevA.111.022808
Open Access Version

Abstract:
The x-ray absorption spectrum of the O+2 molecular cation is measured. The ions are stored in a cryogenically cooled radiofrequency ion trap and probed by tunable synchrotron radiation. The spectrum exhibits several salient features: a three-state composite 𝜋* resonance at the low-energy side followed by a two-component exchange split, a highly dissociative, 𝜎* resonance pulled down well below the ionization limit; and a complex valence-Rydberg high-energy part, including several resolved bands. Small structures are interpreted as correlation state satellites with leading internal or semi-internal configurations. Calculations using the restricted active space wave functions and quantum wave packet dynamics offer an overall excellent interpretation of the spectral features.