Strong non-condon effects induced by electron correlation: N₂O⁺

The vibronic structure of the third band in the photoelectron spectrum of N₂O is investigated. It is shown by ab initio Green's function calculations that there are two ionic states within the energy range of the band which have almost equal spectral intensities due to strong electron correlation. These electronic states interact vibronically through both totally symmetric modes. By adjusting some of the vibronic coupling parameters the experimental results can be qualitatively reproduced. The nature of the vibronic structure is discussed in terms of nonadiabatic and non-Condon effects. The importance of this type of vibronic coupling effects in the inner valence region of ionization spectra is pointed out.