Hidden double excitations in the oxygen inner-shell ionization continuum of CO

Auger decay spectra of CO subsequent to O 1s ionization with 549.85 eV photons, i.e. close to the top of the shape resonance, are presented. Their comparison with the normal Auger spectrum recorded at a photon energy well above the shape resonance reveals distinct features. In particular, in the energy region of the O 1s−1 → b15 and O 1s−1 → a16+ Auger transitions which are well known to consist of vibrational progressions, additional narrow lines are revealed by the spectra recorded at 549.85 eV. In a detailed fit analysis of these Auger spectra it was possible to show that the newly found lines do not exhibit 8 Author to whom any correspondence should be addressed. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New Journal of Physics 15 (2013) 033003 1367-2630/13/033003+13$33.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft