Atomic autoionization observed in nd → σ* molecular resonances

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. The direct experimental evidence of its repulsive character is shown by photoelectron spectroscopy in the case of a d-shell excitation of halogen compounds such as HBr, CH3 Br HI and CH3 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. 13 references, 9 figures