Inner-shell excitation spectroscopy of aniline, nitrobenzene, and nitroanilines

Oscillator strengths for C 1s, N 1s, and O 1s excitation spectra of aniline, nitrobenzene, and the isomeric nitroanilines have been derived from inner-shell electron energy loss spectroscopy recorded under low momentum transfer conditions (>2.5 keV impact energy and small scattering angle, theta less than or equal to 2 degrees). Extended Huckel Molecular Orbital (EHMO) calculations carried out within the equivalent core analogy are used to aid spectral interpretation. These spectra are used to investigate the sensitivity of core excitation spectroscopy to charge transfer interactions in aromatic molecules that have both electron-donating and electron-withdrawing substituents. Strong multielectron excitation features were not found, although these had been anticipated from photoemission studies. The C 1s --> pi* and N 1s (NH2) --> pi* spectral features of the nitroanilines are found to be strongly dependent on the substitution pattern (ortho, meta, or para).