The changes in the valence band and the C 1s core peak and its shake-up satellite of a ${\mathrm{C}}_{60}$ film upon photopolymerization are studied by x-ray photoelectron spectroscopy. It was found that the intensity of the C 1s shake-up satellite of the phototransformed ${\mathrm{C}}_{60}$ film decreased with increasing irradiation time of a 500-W mercury lamp (0–200 h). On the other hand, the valence-band structure of the ${\mathrm{C}}_{60}$ film was almost unchanged even after 200 h of irradiation, compared with that of the pristine ${\mathrm{C}}_{60}$ film. This suggests that the change in the transition probability of each C 1s shake-up satellite peak (π-π transitions) is very small after irradiation and thus plays only a minor role in the reduction of the satellite intensity. The average number of [2+2] cycloadditional four-membered ring structures on a ${\mathrm{C}}_{60}$ molecule was estimated from the decrease in the satellite intensity.

• Received 25 November 1996

DOI:https://doi.org/10.1103/PhysRevB.55.10051