Vibronic coupling and valence mixing in the 1s→Rydberg excited states of C2H2 in comparison with N2 and CO

Abstract

Abstract Angle-resolved ion-yield spectra are reported for the C1s→Rydberg excitations of linear acetylene C 2 H 2 in comparison with N 2 and CO. The 3σ u * valence state is observed in the 3sσ g Rydberg region with no mixing. The 3pσ u state is found in the same region as the C1sσ g →3pπ u state, which shows only totally symmetric vibrations. This is the first to observe that the Rydberg state in C 2 H 2 keeps gerade and ungerade symmetries without vibronic coupling through antisymmetric stretching vibrations related to core–hole localization. On the other hand, the lowest 1π g * valence state induces vibronic coupling through bending vibrations in the 3σ u * and 3sσ g states.