  Photoionization of an atom in the presence of a neighboring atom of different
species is studied. The latter first undergoes resonant photoexcitation,
leading to an autoionizing state of the diatomic system. Afterwards, the
excitation energy is transferred radiationlessly via a two-center Auger process
to the other atom, causing its ionization. Assuming a fixed internuclear
distance, it has been predicted theoretically that this indirect ionization
pathway can strongly dominate over the direct photoionization. Here, we extend
the theory of resonant two-center photoionization by including the nuclear
motion in van-der-Waals molecules. An analytical formula is derived reflecting
the influence of molecular vibrational dynamics on the relative strength of the
two-center channel. For the specific example of Li-He dimers we show that the
two-center autoionizing resonances are split by the nuclear motion into
multiplets, with the resonance lines reaching a comparable level of enhancement
over direct photoionization as is obtained in a model based on spatially fixed
nuclei.
