Energy-dependent vibrational excitation by electron impact in thin films of amorphous benzene

The vibrational excitation of 10-layer films of amorphous solid benzene has been measured by electron-energy-loss spectroscopy at various incident energies between 1.2 and 14.7 eV. The high resolution of the spectra in connection with the energy dependence leads to a comprising assignment of the observed bands. The 2B2g shape resonance is located between 3.2 and 4.2 eV which is about 1 eV lower than in gaseous benzene. The 2E2u resonance is shifted to energies lower than 1.2 eV and is therefore not detected. The e2u vibration, the excitation of which was previously discussed only through the 2E2u resonance channel, is observed at all impact energies.