Use of core electron binding energies for the comparison of valence-shell ionization potentials and the quantification of the bonding and antibonding character of molecular orbitals

A localized-orbital ionization potential (LOIP) is defined as the ionization potential that an atomic orbital would have if it were in a hypothetical nonbonding state and were localized on a particular atom in a molecule. The LOIP includes the entire molecular potential at the atom and the electronic relaxation energy associated with the creation of a positive charge on the atom. It is shown that differences in core electron binding energy between compounds of the same element are proportional to the corresponding difference in LOIP. Thus, it is possible to measure quantitatively the relative bonding or antibonding character of actual molecular orbitals, relative to hypothetical nonbonding atomic orbitals, by using experimental valence and core ionization potentials