AB-INITIO STUDY OF THE ACETYLENE AND VINYLIDENE DICATIONS FRAGMENTATION

The C2H2++ fragmentation processes have been studied using the complete active space self-consistent field method followed by a multireference perturbative configuration interaction, in order to interpret recent charge separation spectroscopy experiments. For two-body processes, the calculated appearance thresholds of the C2H +/H+ and CH+CH- fragment pairs are in good agreement with the experimental data. It is shown that the C 2H2++→CH++CH+ dissociation occurs with an important rotation of the CH+ ions. The presence of the CH2+ ion is explained by a preliminary isomerization- of acetylene to vinylidene dication. This reaction has been studied for the lowest lying states of C2H2- (3Σg- and 1Δ g) and compared with other acetylenic ions isomerizations (C 2H2, C2H2-, C 2H2). For three-body processes, the calculations are consistent with the mechanisms proposed by the experimentalists. © 1995 American Institute of Physics.