Vibrational excitation by electron impact in thin solid films of cyclopropane

Vibrational electron-energy-loss spectra of solid films of cyclopropane have been recorded at different incident energies, scattering angles, and upon changing the sample crystallinity. The intensity variations are exploited for the assignment of the observed vibrational modes. A simple model is used to explain the intensity distribution in the multiple scattering spectral region dominated by twofold loss processes. This model demonstrates that dipole scattering processes may be distinguished from excitation through impact scattering even in completely disordered samples by comparing the intensities of the multiple scattering bands to those of the fundamental vibrations.