Dissociations of the ethyne dication C2H2+2

Dissociations of the ethyne dication following its production by photoionization in the photon energy range of 35–65 eV have been investigated by the photoelectron–ion–ion coincidence technique using both synchrotron radiation and laboratory light sources. New quantum mechanical calculations identify and locate the electronic states of the molecular dication in this energy range and show that the dissociation products are formed in their ground states by heterogeneous processes. Five reaction channels leading to three molecular fragments have been identified and are interpreted as sequential processes, several faster than fragment rotation and one possibly involving dissociation of CH+ to H+ with a lifetime of the order of 25 fs.