Resonance structure in the vibrationally resolved photoelectron branching ratios and angular distributions of the 2π−1 channel of NO

We report on vibrationally resolved measurements of photoelectron angular distributions and branching ratios for NO+(2π−1)X 1Σ+ using synchrotron radiation over hν=11.5–26 eV. Normally weak vibrational levels are strongly enhanced below 18 eV, and the photoelectron asymmetry parameters and branching ratios display a vibrationally dependent, broad spectral structure over hν≂11–18 eV. These observations may reflect the presence of the expected σ shape resonance, however, various interchannel coupling mechanisms may also be involved. Resonance structure in the photoelectron asymmetry parameters is also observed in the hν≂19–22 eV region. This structure is likely associated with Rydberg excitations from the 4σ orbital.