Excited Electronic Levels in Conjugated Molecules: II. On the Symmetry and Multiplicity of Molecular States

Abstract

A comparison of the valence-bond method and the method of molecular orbitals shows that the valence-bond method, while often more reliable for the calculation of ground-state energies, leads to erroneous conclusions as to the number and nature of the excited states, whereas the method of molecular orbitals gives the right number of excited states of any specified symmetry and multiplicity, and leads to semi-quantitatively correct energies for the ground state and lowest excited states. The latter method therefore seems to be the more reliable for the interpretation of electronic absorption spectra in conjugated systems.