A spectroscopic analysis of photochemical processes in fullerenes

Summary form only given. Raman spectroscopy is employed as a probe of photochemical processes in both oxygen-free and oxygenated samples of C/sub 60/. The amplitude of the peaks are observed to be sensitive to light exposuro. Each of the initially observed peaks degrades while new peaks emerge approximately ten wavenumbers to the low energy side. In oxygenated films, the degradation process is observed to be apparently slower. The process is analysed in terms of the population of the triplet state leading to sample degradation competing with the ground state recovery in an attempt to elucidate the mechanism of fte photochemical process, proposed to be a 2+2 cycloaddition in which oxygen acts to inhibit the photochemical degradation via a triplet quenching. Particular attention is paid to the dependence of the process on input light intensity. The degradation is further reported to be highly dependent on the substrate employed. At high intensities, a further change in the Raman stectrum is observed, the peals abruptly shifting to a frequency intermediate -between those of the photoproduct and of pristine C/sub 60/. The shift is accompanied by a dramatic increase in the Raman intensity. Upon reduction of the intensity, the C/sub 60/ spectrum is recovered, indicating that the photochemical process is reversible under high intensity illumination. The nature of the high intensity intermediate is discussed.