The valence character of O 1s→Rydberg excited O2 is investigated by means of participator Auger decay spectroscopy, performed at selected photon energies across the K -shell resonance region, and by means of partial ion yield x-ray absorption spectroscopy. For several of the excitation energies studied, the authors find substantial * (u-4, u-2) valence character being mixed with ns and np (u-4, u-2) Rydberg states. An experimental indication of a coupling between the channels associated with quartet and doublet ion cores is considered and discussed. New spectroscopic constants are derived for the singly ionized X Πg2 state of O2 based on the observation of at least 20 vibrational sublevels.
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