ELECTRON-ENERGY-LOSS SPECTROSCOPY IN MONOSUBSTITUTED BENZENES

The electron energy-loss spectra of toluene, monochlorobenzene, phenol, nitrobenzene and aniline vapours have been obtained at 70 eV impact energy and 0 degrees scattering angle. Interpretation of the spectra has been attempted with the aid of previous experimental data and quantum chemical calculations in the literature. The excited states observed are generally in good agreement with those obtained in vacuum ultraviolet optical absorption studies. In extending the measurements beyond the first ionization potentials, unreported transitions have been obtained and are assigned to Rydberg states on the basis of term values with respect to ionization potentials determined by photoelectron spectroscopy. Apparent optical oscillator strength distributions were derived from the energy-loss data under the assumption that the Born approximation is valid at energies as low as 70 eV.