Nature of the one electron energies of the independent electron molecular orbital theory and of the Walsh diagrams

Abstract

It is suggested that the “one electron energy” or “binding energy” of the independent electron molecular orbital theory is the change in the ionization energy of the molecular orbital on molecule formation. This interpretation is discussed in the context of the Walsh diagram for the water molecule. The general method is to reduce the self-consistent field molecular orbital theory to the independent electron theory by systematic approximations and by appeal to physical arguments.

Broadly speaking, the results support Walsh's method of constructing his diagrams but they also show that it is important to distinguish clearly between ionization energies and binding energies and also between the different types of delocalized molecular orbital. If these distinctions are not made, one may emerge with a diagram which is a mixture of several different but related diagrams. Walsh's original diagrams seem to be based on an unusual type of delocalized molecular orbital. The work also gives a clear definition of the terms bonding, non-bonding and antibonding molecular orbitals.