PHOTON-INDUCED INTERMOLECULAR COUPLING IN ULTRATHIN C-60 FILMS

Raman spectra of ultrathin C60 films on SiO(x) (x approximately 2) in ultrahigh vacuum show strong irradiation-induced changes that persist but decay with time (2-3 h). The induced changes are suppressed upon c ooling (120 K) and additional changes are introduced with heating (600 K). The observation of induced low-energy vibrational bands between t he molecular and lattice vibrational spectrum suggests intermolecular bond formation. Application of the semiempirical interatomic Tersoff p otential to estimate the intermolecular coupling reveals that the inte ratomic potential for C60 differs strongly from that between two graph itic sheets and it is suggested that weak intermolecular covalent bond s are formed.