The Dissociative Ionization of C2H2. The C+, C2+ and CH2+ Dissociation Channels. The Vinylidene Ion as a Transient?

The dissociative electroionization of C2H2 has been investigated in the C+, C2+ and CH2+ dissociation channels. Both the translational energy and the appearance energies have been measured. The kinetic energy versus appearance energy diagrams related to these species are discussed in detail and dissociation mechanisms are proposed for all observed onset energies. For the three ionic species, the dissociation pathways leading to the fragmentation of C2H2+ into C+, C2+ and CH2+ successively have to run very likely over an isomerization mechanism of the molecular ion. The isomeric vinylidene structure could be the most probable intermediate.