Vibrationally resolved shape resonant photoionization of N₂O

We report a vibrationally resolved dispersed fluorescence study of 7σ^-1 shape resonant photoionization in N₂O. Previous work indicates that there are two shape resonances in the εσ channel, and our results demonstrate that the lower energy shape resonance (hv_exc ≈ 20 eV) results in non-Franck-Condon vibrational branching ratios over a wide range. Moreover, the cross section curves for alternative vibrational modes behave differently, and we show that the symmetric stretch exerts a greater influence on resonance behavior than the asymmetric stretching vibration. Such comparisons of vibrationally resolved partial cross section curves provide qualitative insights into the shape resonant photoionization dynamics for polyatomic targets. The higher energy shape resonance is apparently masked by the presence of the dominant nonresonant επ channel. In addition to information on the photoionization dynamics, these results also provide spectroscopic data on the ionic potential surfaces. Specifically, we obtain ratios of Franck-Condon factors for N₂O⁺ (A → X) transitions which are useful for testing calculated properties of the ion.