Photoinduced structural changes in crystalline C60:: relaxation of exciton and dimerization processes

We numerically investigate the lattice relaxation of photogenerated exciton in crystalline C-60 so as to clarify the mechanism of the photo-induced dimerization in this material. In our theory, we deal with the pi-electrons together with the interatomic effective potentials. Calculations are mainly based on the mean-field theory, but are also reinforced by taking the electron-hole correlation into account, so that we can obtain the exciton effect. We calculate the adiabatic potential energy surfaces of the Frenkel and the charge transfer (CT) excitons relevant to the photoinduced dimerization occurred in a FCC crystal of C60 These potentials lead to the conclusion that various structural defects exist at low temperatures even in the single crystal, as an intrinsic property of this molecular crystal. Moreover, it is confirmed that the CT exciton relaxes down to its self-trapped state which triggers the photodimerization. (C) 2000 Elsevier Science B.V. All rights reserved.