Shape resonance and non-Franck–Condon behavior in the photoelectron spectra of O2 produced by (2+1) multiphoton ionization via 3sσ Rydberg states

Photoelectron spectra produced by (2+1) MPI via the v=0–3 levels of the (3sσg ) C 3 Πg Rydberg state of O2 show large deviations from the Franck–Condon principle. These deviations are attributed largely to a shape resonance in the σu ionization channel and probably a ‘‘window’’ resonance in the 3 Σ−u part of the πu channel.