Electronic, rotational and vibrational predissociations in the decay of electronically excited molecular ions

Abstract

A review is made of experimental and theoretical studies about the occurrence of electronic predissociation processes either allowed or forbidden, in the dissociation of CH+ , [Math], CO+ , [Math], NO+ [Math] and N2 O+ . The importance of rotational predissociation is emphasized in the dissociation of diatomic ionized hydrides and its occurrence in the decay of [Math] brings attention to the possibility that such a process could play an important role in the apparance of metastable ions in the mass spectra of complex molecules, especially when the loss of H or H2 is involved. The discussion, with the help of correlation diagrams, of some dissociation channels of C2 H3 F+ and CH3 OH+ , shows the coexistence in these mechanisms of adiabatic processes, principally due to the occurrence of avoided crossings” or of conical intersections and of non-adiabatic processes such as electronically forbidden predissociations. The role of autoionization in the population of dissociation processes has been emphasized each time it was involved.