Photoionization Decay of Core Excited Molecules

The excitation of a core electron into an antibonding empty valence orbital of a molecule leads to a quite intense resonance compared to Rydberg transitions in the photoabsorption spectrum. We show the direct experimental evidence of its repulsive character by photoelectron spectroscopy in the case of a d -shell excitation of halogen compounds such as HBr, CH 3 Br, HI and CH 3 I. The first step of the resonance decay is a very fast dissociation process followed by autoionization of the core excited fragment as a second step. Competition with usual molecular autoionization is found when the mass of the radical linked to the excited atom is increased.