Ab initio CASSCF and MRSDCI calculations of the (C6H6)2+ radical

Ab initio complete active space self-consistent field (CASSCF) and multireference singly and doubly excited configuration interaction (MRSDCI) calculations were performed for the (C6H6)2+ radical. The calculations revealed that the global minima of the ground state of (C6H6)2+ are at distorted C2h geometries. Sandwich (D6h) and T-shaped (C2v) structures are higher in energy than the minima by 0.4 and 3.7 kcal/mol, respectively. The calculated binding energy is 15.0 kcal/mol compared with an observed value of 20.6±1.0 kcal/mol. The excitation energies of low-lying excited states are discussed.