VIBRONIC STRUCTURE AND RESONANCE EFFECTS IN THE OPTICAL-SPECTRA OF THE FULLERENES C-60 AND C-70

Optical emission spectra of solid C-60 and C-70 were recorded at 1.9 K using different detector systems. In the region of low energy an improved resolution could be obtained using an IR sensitive photodiode. The energy of the emitting states of C-60 was estimated by means of resonant excitation using a dye laser. The proposed assignment of the vibrational fine structure is based on vibrational frequencies obtained from normal coordinate analysis and CNDO/S-calculated intensities of false origins, both reported in the literature. It is shown that the emission arises from two electronic states. Low-energy excitation of C-70 supplies evidence for two emitting states as well. Resonance excitation supplies specific changes of the emission spectrum attributed to different excited levels.