DISSOCIATIONS OF THE ETHYNE DICATION C2H22+

Dissociations of the ethyne dication following its production by photo ionization in the photon energy range of 35-65 eV. have been investiga ted by the photoelectron-ion-ion coincidence technique using both sync hrotron radiation and laboratory light sources. New quantum mechanical calculations identify and locate the electronic states of the molecul ar dication in this energy range and show that the dissociation produc ts are formed in their ground states by heterogeneous processes. Five reaction channels leading to three molecular fragments have been ident ified 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.