Multiplet-specific shape resonant features in vibrationally resolved 3σ_g photoionization of O_2

Abstract

We report multiplet‐specific vibrationally resolved photoionization cross sections and photoelectron angular distributions for the 3σ_g orbital of O_2 leading to the v^+=0–3 levels of the b^4Σ^−_g and B^2Σ^−_g states of O^+_2. These studies were motivated by recent work which shows significant nonstatistical behavior in the vibrationally unresolved spectrum at low photoelectron energies arising from the sensitivity of the kσ_u shape resonance to the multiplet‐specific exchange potentials. In addition to the anticipated non‐Franck–Condon vibrational distributions arising from the kσ_u shape resonance, we also find substantial nonstatistical effects in our vibrationally resolved cross sections and particularly in our photoelectron angular distributions over a broad energy range. Extensive electronic autoionization due to Rydberg levels leading to the c^ 4Σ^−_u (2σ^(−1)_u) ion makes it difficult to assess these effects in the available experimental data.