Photon-assisted synthesis of C60 polymers by laser irradiation

The harmonics of a free electron laser (FEL) were irradiated in vacuum to surfaces of compressed C60 and a mixture of C60 and I2. The power and frequency of the fundamental FEL macro-pulse were ca. 0.5 mJ/pulse and 2 Hz, respectively. The irradiation time was 120-180 min. After irradiation of FEL with a typical wavelength of 450 or 345 nm, the Raman peak of Ag(2)-derived vibration mode of C60 shifted to the lower-energy side. The Raman peak shift of the mixture powder sample was greater than that of pure C60. Furthermore, changes of the crystalline structure indicated that various intermolecular combinations occurred by irradiation. These results strongly suggest that three-dimensional polymerization of C60 was promoted by laser irradiation and the effect of photon-assisted hole-doping from iodine atoms to C60 molecules.