Photoelectron Spectra of Polymers

The calculated ionization potentials enable one to interpret the measured X-ray photoelectron spectra (XPS) of polymers. The Namur group has performed a series of investigations in this field (a review has been published elsewhere ). To be able to compare an experimental valence electron XPS with a theoretical spectrum, the intensities of the different peaks are also needed for the construction of the theoretical spectrum besides the IPs (the energy difference between the iV — 1 and N electron states). (Actually, XPSs are more important in the identification and determination of different elements in a material. For an experimental check of the calculated band structures of an organic polymer, however, the valence electron XPSs have to be used.) 

In comparing an experimental and theoretical XPS one should not forget that the experimental XPS contains three contributions, which originate from three different physical processes  

Excitation of an electron from an initial state ei(k) to the final one 

However, since the structure (both bulk and surface) of most polymeric solids is rather ill-defined, there seems to be no hope of treating theoretically, in the near future, steps (2) and (3) and hence finding out the energies necessary for these steps. Therefore, all authors restricted themselves to step (1) and nearly always applied all-valence semiempiri- 

For the ionization potential, all these calculations have applied the Koopmans theorem in its simple form 

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