Structure and bonding of the (C6H6)+ 2 radical

Abstract

To elucidate the relative stability of various structures of the benzene dimer cation radical, (C6H6)+ 2 in its ground and low-lying excited states, ab initio complete active space self-consistent field (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations were performed. Full optimization was performed at the CASSCF level for various structures of the dimer cation, followed by MRSDCI and MRCPA calculations. It was found that the global minimum of the cation is at a slipped C2h sandwich structure but there are some other sandwich structures with almost the same stability, being within about kcal mol−1. T-shape structures are less stable than the sandwich structures, by more than 5 kcal mol−1 by MRCPA calculations. Low lying electronic excited states in various structures are also discussed.