Global Franck-Condon breakdown resulting from Cooper minima

Abstract

Using N2 2σu-1 photoionization as an example, we present the first measurements and calculations of photoion vibrational distributions for an extended energy range ( 5≤Ek≤230 eV). The results show a striking breakdown of the Franck-Condon approximation over a 100 eV range. We show that this coupling between vibrational and electronic motion arises from a dependence of Cooper minima on molecular bond length. Based on this mechanism, the effect is expected to be common for molecular systems.