Dimer and cluster formation in C-60 photoreaction

The process of phototransformation in C-60 was analysed by means of Raman spectroscopy for single crystals irradiated at various temperatures between 80 K and 450 K. The activation window for the transformation process was found to be between the temperature of the first order phase transition of 260 K and an upper temperature of about 400 K. Detailed features of the resulting spectra were found to depend on the transformation temperature. From a comparison with ab initio calculations of Porezag et al. the material irradiated at high temperatures could be assigned to a C-60 dimer whereas the material phototransformed at room temperature could not be identified with a simple cluster.