RAMAN-SCATTERING IN ELECTRONICALLY EXCITED C-60

The low-temperature Raman spectrum of 2a0-fcc single crystal C60 recorded using low-irradiance 514 nm excitation shows only a single peak in the region of the 1468 cm-1 out-of-phase ring mode. For higher irradiances a new broad peak appears in the spectrum at a somewhat lower frequency. Simultaneously, an increase of the luminescence is observed. As the irradiance increases the new peak gains intensity and shifts to lower frequencies, whereas the original peak slowly disappears. It is argued that this peak originates from electronically excited C60. A simple electronic four-level model is proposed to explain the observed effects.