The angularly resolved O 1 s ion-yield spectrum of O₂ revisited

The high-resolution photoabsorption spectrum of O₂ below the O 1sσ-1 ionization threshold has been reanalyzed by using a sophisticated fit approach. For the vibrational substates of the O 1sσu-1(4 u-)3sσg(3 u-) Rydberg state Fano lineshapes are observed indicating an interaction with the O 1sσg-1(4 g-)3σu- (3 u-) core-to-valence excited state. In the angularly resolved ion-yield spectrum recorded at 90° relative to the polarization direction of the synchrotron radiation clear evidence for the O 1sσg-1(2 g-)3σu- (3 u-) and the O 1sσu-1(2 u-)3sσg(3 u-) state was found. This observation clearly suggests thatΛ, the projection of total orbital angular momentum on the molecular axis, is not well separated in the angularly resolved ion-yield spectrum due to a partial breakdown of the axial-recoil approximation for these transitions.