Have the ions C2H+3 and C2H+5 classical or non-classical structure?

Abstract

Calculations based on the independent-electron -pair approximation (including intra- and inter-pair correlation effects) were performed for the ground state of acetylene, ethylene and their protonated cations. The classical and non-classical (bridged) structures were considered for the cations. The results of the calculations indicate that the bridged forms are lower in energy by about 7 kcal/mole and 9 kcal/mole for C2H+3 and C2H+5, respectively. This is mainly due to the larger correlation energy for the non-classical forms. On Hartree-Fock level (including polarization functions) the classical and non-classical structures of C2H+5 have practically the same energy. For C2H+3 the inclusion of correlation effects reverses the relative stability of the two structures.