Electronic structure of octavinyl- and octaphenylsilsesquioxane from XPS and DFT data

X-ray photoelectron spectroscopy (XPS) and density functional theory are employed to study the electronic structure of octasilsesquioxanes (RSiO_1.5)₈ with vinyl and phenyl terminal groups. Quantitative compositions determined from the XPS data are close to those estimated by empirical formulas. Narrow spectral lines corresponding to ionization from C1 _s core levels indicate similar chemical states of carbon atoms for both compounds. Experimental data are confirmed by close calculated values of effective charges on carbon atoms when polarization functions are included in the basis set and also by small energy ranges of core level electrons. The valence spectral region is interpreted based on the calculated energy values of electronic levels with regard to the density of states and ionization cross-sections.