Mechanisms of Franck-Condon breakdown over a broad energy range in the valence photoionization of N2 and CO

► We measured the vibrational branching ratios for the photoionization of N2 and CO. ► We computed the corresponding branching ratios for the X and B ion states. ► The logarithmic derivative of the cross section was used in the comparison. ► Non-Franck-Condon effects were seen due to Cooper minima. ► The Cooper minima were related to Cohen-Fano interference effects.