Importance of Doubly Excited Configurations in the Interpretation of Electronic Spectra

Abstract

An investigation has been carried out to determine the importance of doubly excited configurations in calculating the energies of the electronic states of an aromatic hydrocarbon. It is found that the calculated low energy states of benzene are largely unaffected by consideration of doubly excited states, except for the appearance of an E_2g state with energy comparable to that of the E_1u states. In addition, inductive and mesomeric shifts in the lowest energy (α) transition have been calculated for all the distinct positions of substitution in benzene, in terms of two parameters which depend on the substituent. It is seen that the inclusion of doubly excited states in the calculation is necessary in order to predict these effects reliably.