Shape resonance influence on the photoelectron angular distributions from O2 C 3Πg, v=0–3

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Abstract
Vibrationally resolved, photoelectron angular distributions are reported for the (2+1) REMPI of the C 3Πg(3sσg), v’=0–3 Rydberg levels of O2. Ionization transitions leading to different vibrational final states (v+) of O+2 exhibit markedly different angular distributions, suggesting different ionization mechanisms. The experimental data are qualitatively reproduced by very recent ab initio calculations which attribute the non‐Franck–Condon behavior to the presence of a kσu shape resonance imbedded in the ionization continuum. Much of the remaining anomalous behavior is attributed to a Fano‐type resonance in the Πu channel.