Butterfly C2H2++:: New way for the decomposition of the acetylene dication

Using highly correlated ab initio methods, a new transition state is characterized in the lowest singlet potential energy surface of HCCH++. This transition state possesses a dibridged (or "butterfly") form not observed yet for any acetylic compound. It can be reached either directly or after spin-orbit conversion of triplet HCCH++ ions. In light of these calculations, a reaction pathway for the proton pair formation (i.e., HCCH++-> C-2+H++H+) is proposed. (c) 2007 American Institute of Physics.