The XPS of azines: A comparative study

A detailed analysis is presented of the X-ray Photoelectron Spectroscopy (XPS) of thin films of three azines: pyrazine, pyridine, and pyrimidine. This includes not only the binding energies of the various core ionizations but also their intensities. A major focus is to compare our theoretical predictions with our measured XPS for N(1s) and C(1s) as a basis for assigning the features and for justifying the broadening parameters that must be applied to the theoretical results. The C(1s) XPS of pyridine and pyrimidine are significantly broadened because of unresolved XPS for their inequivalent C atoms. The extent of the binding energy (BE) shifts and the XPS intensities for the unique C atoms, which are responsible for this broadening, are obtained from the theory. The additional broadening parameters to be applied to the theory to enable comparison with measured XPS are discussed in terms of lifetime broadening, experimental resolution, and BE shifts in different layers of the thin film. A novel feature of our analysis is that we have investigated and justified the broadenings necessary to make of the calculated BEs in order to fit the observed XPS spectra. The results presented have general value for extracting chemical and physical information from XPS.