Global Franck-Condon breakdown resulting from Cooper minima.

Kwanghsi Wang and V. McKoy Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125 (Received 1 December 1995) Using N2 2s21 u 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.