Investigation of the low energy optic excitations in crystalline C_60

摘要

The low energy optic excitations in crystalline C_60 are investigated by linear and non-linear spectroscopic techniques. Two-photon excitation directly locates the lowest purely electronic 0-0 transition at 14 850 cm~(-1). By the analysis of the Herzberg-Teller induced photoluminescence the lowest forbidden Frenkel exciton is assigned to a T_1g excited state. At low temperature, the absorption spectrum exhibits doublet features with constant energetic splitting. The two distinct alignments of neighbouring C_60 molecules (merohedral order) might be responsible for the double resonances.