Photoionization/fragmentation of endohedral fullerenes

Photoionization/fragmentation of endohedral fullerenes was investigated by use of laser-desorption time-of-flight (LD-TOF) mass spectroscopy. The velocity distribution of the parent ion (LaC₈₂⁺) was found to be bimodal, as has previously been shown for laser desorbed C⁺₆₀. The fragment ions have velocity distributions corresponding predominantly to the fast parent ion distribution. The LD-TOF mass spectra taken with a relatively low laser fluence were independent of the delay time of the extraction pulse, showing only a monotonically decreasing pattern of LaC_2n⁺ (as n decreased). However, with higher laser fluence, it was shown that the mass distributions drastically changed from the monotonically decreasing pattern to that of C_2n⁺ and LaC⁺_2n with magic numbers. Based on these findings, a plausible photoionization/fragmentation mechanism is presented and discussed.