The intramolecular charge-transfer interaction in X-ray photoelectron spectroscopy: the charge-transfer satellites observed in p-nitroaniline and related compounds

Abstract

For highly-polar nitro-substituted aromatic compounds, characterization of the nitro-N 1 s core-hole states from the standpoint of intramolecular charge-transfer (CT) interaction is obtained through analysis of the energy difference between the satellite and the main peak, and the relative intensity of the satellite compared to the main peak. Two-dimensional configuration interaction (CI) is considered between the no-bond (covalent) and the CT (ionic) structures in both the initial and the final states. The off-diagonal element between these two structures is given in terms of the core resonance integral between the ring carbon and the nitro nitrogen, and can therefore be reduced by steric hindrance, and is also closely related to the π-electron density at the adjacent carbon in the donor orbital. The absolute magnitude of the off-diagonal element and the ionization potential of the donor are important factors determining the relative intensity of the CT satellite. It was found that in the case of some nitro-N 1 s core-hole ions the CT structure is located below the no-bond structure, and that two-dimensional CI calculations are valid as far as the ground and the CT states are concerned.