Shape resonance and non-Franck–Condon effects in (2+1) resonant enhanced multiphoton ionization of O2 via the C 3Πg state

Abstract

We report vibrationally resolved photoelectron angular distributions for photoionization of the C ³Π_g Rydberg state of O₂. Comparison is made with recent experimental measurements of angular distributions which employ (2+1) resonant enhanced multiphoton ionization of the C ³Π_g state. The present theory treats the process as single‐photon ionization from an unaligned Rydberg state, and qualitatively accounts for much of the observed trends. Non‐Franck–Condon effects induced by the kσ_u shape resonance lead to a substantial dependence of the angular distributions on the vibrational state of the X ²Π_g ion. Discrepancies between our theoretical results and experiment are qualitatively discussed and tentatively attributed to residual electron correlations.