Ion-induced molecular fragmentation: beyond the Coulomb explosion picture

The fragmentation of the CO molecule by O7+ ion impact is investigated in t wo different energy regimes by fragment ion momentum spectroscopy. The impr oved resolution of the present kinetic energy release measurement together with application of a time-dependent wavepacket dynamics method used in con junction with new high-level computations of a large number of dication pot ential energy curves enables one to unambiguously assign each line to an ex cited state of the transient molecular dication produced during the collisi on. This is the first direct experimental evidence of the limitations of th e Coulomb explosion model to reproduce the molecular fragmentation dynamics induced by ion impact. Electron removal due to a capture process is shown to transfer less excitation to the target than direct ionization. At low co llision velocity, the three-body interaction between the projectile and the two fragments is also clearly highlighted.