C 1s and N 1s core excitation of aniline: Experiment by electron impact and ab initio calculations

Core shell excitation spectra of aniline at the carbon and nitrogen 1s edges have been obtained by inner-shell electron energy-loss spectroscopy recorded under scattering conditions where electric dipolar conditions dominate, with higher resolution than in the previous studies. They are interpreted with the aid of ab initio configuration interaction calculations. The spectrum at the C 1s edge is dominated by an intense pi(*) band. The calculated chemical shift due to the different chemical environment at the carbon 1s edge calculated is in agreement with the experimental observations within a few tenths of an eV. The transition energies of the most intense bands in the C 1s excitation spectrum are discussed at different levels of calculations. In the nitrogen 1s excitation spectrum the most intense bands are due to Rydberg-valence transitions involving the sigma(*)-type molecular orbitals, in agreement with the experiment. This assignment is different from that of extended Huckel molecular orbital calculations. The geometries of the core excited states have been calculated and compared to their equivalent core molecules and benzene.