Anomalous Photofragmentation of Fullerene Doped in Silica Aerogel-Enhanced Formation of Odd-Numbered "Fullerene" Fragments

Photofragmentation of fullerene-doped silica aerogels has been investigated by the excimer laser ablation reflectron time-of-flight mass spectrometric technique. Great enhancement in the formation of odd-numbered ‘fullerene’ fragments has been observed in the negative-ion channel for the chemically doped aerogel sample. Generally, oddnumbered species C57, C55, C53 and C51 appeared in the mass spectra. Under optimM experimental conditions C55 can be even more intense than the neighbouring even-numbered carbon clusters. In contrast, for the physicallydoped sample, just like pristine C6o, only weak odd-numbered fragments were observed. In the positive-ion channel, the behaviour of all these samples is similar, no odd-numbered species was ever detected. A mechanism related to the interaction between the fullerene dopant and the silica aerogel host is suggested for the anomalous enhancement of the odd-numbered duster formation. A preliminary discussion on the structures of the oddnumbered‘fullerene’ fragments is given.