Strongly perturbed Stark states and electron correlation in Ba

We present the results of experimental and theoretical investigations into the photoionization spectra of Ba Stark states at energies resonant with th e 5d7d D-1(2) perturber level starting from the 5d6p D-3(1)o state. The ele ctric field is strong enough to allow the electrons to classically escape t he atom, thus transforming the perturber state into a resonance. Much of th e dynamics of this remarkably complex system may be understood qualitativel y. In particular, we stress the role played by electron escape time in qual itatively changing the correlation by reducing the singlet-triplet mixing a nd triplet excitation. A theoretical formulation of multichannel systems in static electric fields is developed which allows us to efficiently obtain both total and partial cross sections; this formulation can be used to desc ribe the Rydberg states of atoms and molecules in static electric fields. [ S1050-2947(99)11308-8].