Molecular Orbital Calculations of the Lower Excited Electronic Levels of Benzene, Configuration Interaction Included

The lower excited π-electron levels of benzene are calculated by the non-empirical method of antisymmetrized products of molecular orbitals (in LCAO approximation) including configuration interaction. All configurations arising from excitation of one or two electrons from the most stable configuration are considered, and all many-center integrals are retained. The results are in better agreement with experiment and valence-bond calculations than those obtained previously by Craig in a calculation neglecting many-center integrals. Configuration interaction is found to change the order of the 1B1u and 1E2g states but leave unchanged the order of the 3B1u and 3B2u states, in agreement with the assignments 1A1g—3B1u and 1A1g—1E2g for the experimental bands at 3.8 and 6.2 ev.