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, odd-numbered species C₅₇, C₅₅, C₅₃, C₅₁ appeared in the mass spectra. Under optimal experimental conditions C₅₅ can be even more intense than the neighboring even-numbered carbon clusters. In contrast, for the physically doped sample, just like pristine C₆₀, 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 cluster formation. A preliminary discussion on the structures of the odd-numbered ‘fullerene’fragments is given.