OSCILLATOR-STRENGTHS OF INFRARED ACTIVE VIBRATIONS OF C-70 DETERMINEDBY HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY

The intramolecular vibrations of a C-70 epitaxial film have been studi ed by high-resolution electron energy-loss spectroscopy (HREELS). The spectral response of infrared active vibrations has been separated fro m the specular spectra based on a detailed angular distribution analys is of the scattered electrons. With the help of the oscillator frequen cies and the damping ratios determined by optical absorption measureme nts, the oscillator strengths of the C-70 dipole active modes between 400 and 1500 cm(-1) are accurately determined by fitting the dipole co ntributions of the HREELS spectrum in the framework of the dielectric theory. Moreover, our experiment confirms that there are infrared acti ve vibrations below 400 cm(-1), which were predicted by molecular dyna mical calculations for C-70.