Observation of strong Rydberg–valence mixing in the E 3Σ-u state of O2 by 3+1 MPI photoelectron spectroscopy.

The photoelectron spectrum (PES) of the E 3Σ-u state of O2 has been measured with 3+1 multiphoton ionization (MPI). The observed vibrational progression in the PE spectrum is interpreted as due to ionization from a (3pπ)3Σ-u Rydberg state which is strongly mixed with the (πu 3π3g)B 3Σ- valence state. The observation of this mixing is in near agreement with the calculation by Buenker et al. [ABSTRACT FROM AUTHOR]