Symmetry and vibrationally resolved absorption spectra near the NK edges of N₂O: Experiment and theory

In this study, angle-resolved energetic-ion yield spectra were measured in the N 1s excitation region of N₂O. A Franck-Condon analysis based on ab initio two-dimensional potential energy surfaces of the core-excited Rydberg states, which were calculated by the symmetry-adapted cluster-configuration interaction method, reproduced observed vibrational excitations specific to the individual Rydberg states well and enabled quantitative assignments. Geometric changes in the terminal nitrogen N_t 1s and the central nitrogen N_c 1s excited states with respect to the 3pπ, 3pσ, and 4sσ transitions were analyzed. The coupling of these valence and Rydbergs states was examined based on the second moment analysis. Irregular Rydberg-state behavior in the N_c 1s^-1 4sσ state was observed.