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Raman Shift (cm )

tral features of the phototransformed film, showing a broad Raman line at 1459 cm-1 associated with the Ag(2) mode of C^, perturbed by the formation of dimers, trimers, and higher oligomers [11.156]. As the temperature is increased, the narrow Ag(2) line at 1469 cm-1 grows at the expense of the broad 1459 cm-1 line, indicating a transformation back to the monomeric solid by a thermal detachment of C60 monomers from the oligomers. The competition between the photoinduced attachment of Qo monomers to form oligomers and the thermal detachment process to form monomers is shown in Fig. 11.35 by plotting the temperature dependence of the integrated intensity of the 1459 cm-1 feature associated with the polymerized phase and the corresponding intensity of the 1469 cm-1 sharp Raman line associated with the C60 monomer [11.156]. The solid curves in this figure are a fit of the rate equations for oligomer formation by the phototransformation process which competes with the thermal dissociation process for monomer formation. Detailed fits of the model to the experimental data show that the rate constant for polymerization is dependent on the photon flux and wavelength, as indicated by the inset to Fig. 11.35 showing the dependence of the fractional monomer population (FMP) in the photopoly-merized film on both temperature and incident light flux <t>0 at 488 nm. An

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