Rotational dependence of the Rydberg–valence interactions in the 1Πg states of molecular oxygen

The two-photon d 1Πg(v′)← ←X 3Σ−g(v″) transition in O2 is studied using resonance enhanced multiphoton ionization (REMPI) spectroscopy and the lowest four vibrational levels of the d 1Πg Rydberg state are characterized. Anomalies in the rotational constants of the Rydberg vibrational levels and perturbations in the REMPI spectra are attributed to the interaction of the Rydberg state with a bound diabatic 1Πg valence state. The rotational dependence of the Rydberg–valence interaction is explored by solving the coupled eigenvalue equations describing the interaction of the two states. The results from solution of the coupled equations as well as observations from photoelectron spectroscopy experiments are used to understand the additional structure seen in the REMPI spectra in the vicinity of the v′=2 Rydberg vibrational level.