The Relationship Between Spectroscopy and Bonding

In this paper we discuss several methods for relating electron spectroscopy and bonding in molecules with the intention to find as direct relation as possible between these quantities. The field of photoelectron spectroscopy seems to provide a new possibility to establish such a relation. The photoemission spectrum in the far ultraviolet is related to the one-electron spectrum, whereas the Auger spectrum contains information about the electron-electron interaction. Two different schemes are discussed in the paper. In the first scheme a theory reminiscent of the Landau-Fermi liquid theory is developed. The total energy is calculated from the relaxed peaks in the photoemission spectra and the pairwise interaction between the electrons is obtained from the Auger spectrum. In the second method we use the full spectral profile obtained from the photoelectron spectrum together with the Auger spectrum to calculate the total electronic energy. The binding energy is obtained by substracting the energy obtained from the corresponding spectra for the constituent atoms. Thus both methods require that the spectra of both the molecule and the free atoms are known with very high accuracy in order to obtain the binding energy. The present experimental accuracy seems high enough to apply the methods developed in this paper. However, the experimental data available at the present time in the literature do not seem accurate and consistent enough to apply these methods and give only an order of magnitude estimate for the binding energy of simple molecules.