THE C4H6-CENTER-DOT-ENERGY SURFACE - 2 - THE REACTION OF ETHYLENE RADICAL-CATION WITH ACETYLENE( POTENTIAL)

The reaction of the ethylene radical cation (Et.+) with acetylene (Ac) to form stable C4H6.+ intermediates and the subsequent fragmentation of these to C3H3+ + CH3. or to C4H5+ + H-. have been studied by the UM P2, RMP2, and B3LYP methods with the 6-31G basis set, as well as by s ingle-point calculations at the RCCSD-(T)/cc-pVTZ level of theory. The aim of this study was to identify all stationary points that might be relevant to explain the course of the observed reactions. According t o their stability to dissociation, we distinguish three classes of C4H 6.+ structures: weakly bonded complexes, structures of medium stabilit y, and tightly bonded complexes. Methylcyclopropene radical cation see ms to be the most likely ultimate precursor for the formation of the o bserved fragmentation products.