OSCILLATOR STRENGTHS OF INFRARED ACTIVE VIBRATIONS OF C70 DETERMINED BY HIGH-RESOLUTION ELECTRON ENERGY-LOSS SPECTROSCOPY

Abstract

The intramolecular vibrations of a C 70 epitaxial film have been studied by high-resolution electron energy-loss spectroscopy (HREELS). The spectral response of infrared active vibrations has been separated from the specular spectra based on a detailed angular distribution analysis of the scattered electrons. With the help of the oscillator frequencies and the damping ratios determined by optical absorption measurements, the oscillator strengths of the C 70 dipole active modes between 400 and 1500 cm −1 are accurately determined by fitting the dipole contributions of the HREELS spectrum in the framework of the dielectric theory. Moreover, our experiment confirms that there are infrared active vibrations below 400 cm −1, which were predicted by molecular dynamical calculations for C 70.