The angularly resolved O 1s 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 1sσ−1u(4∑−u)3sσg(3∑−u) Rydberg state Fano lineshapes are observed indicating an interaction with the O 1sσ−1g(4∑−g)3σ∗u(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 1sσ−1g(2∑−g)3σ∗u(3∑−u) and the O 1sσ−1u(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