GLOBAL FRANCK-CONDON BREAKDOWN RESULTING FROM COOPER MINIMA

Using N-2 2 sigma(n)(-1) photoionization as an example, we present the first measurements and calculations of photoion vibrational distribut ions for an extended energy range (5 less than or equal to E(k) less t han or equal to 230 eV). The results show a striking breakdown of the Franck-Condon approximation over a 100 eV range. We show that this cou pling between vibrational and electronic motion arises from a dependen ce of Cooper minima on molecular bond length. Based on this mechanism, the effect is expected to be common for molecular systems.