Ab initio CASSCF and MRSDCI calculations of the (C 6H 6) 3+ radical

Abstract

Ab initio complete-active-space self-consistent-field (CASSCF), single-reference singly and doubly excited configuration interaction (SRSDCI), and multi-reference SDCI (MRSDCI) calculations were performed for the benzene trimer cation, (C 6H 6) 3 +, in its ground state. We found that the global minimum of the cation is the distorted C 2v sandwich structure, which is 0.032 eV lower than the D 6h sandwich structure. The dissociation energy ( D e) relative to (C 6H 6) 2 ++C 6H 6 was calculated to be 0.43 eV, in comparison to the experimental value ( D 0) of 0.34±0.02 eV. Our calculations revealed that most of the charge of the trimer cation is localized in the central benzene ring, whose gross charge is +0.9. The low-lying excited states arising from the π–π transition are also discussed.