LASER MASS SPECTROSCOPIC INVESTIGATIONS OF PURIFIED, LABORATORY-PRODUCED C60/C70

Laser desorption mass spectra of Kratschmer's purified "fullerite" have been studied in a reflectron time-of-flight mass spectrometer, Desorption with 308 or 248 nm yields direct ions emerging from the substrate with high efficiency. At low fluence, a distribution of pure C60+ (76%), C70+ (23%) and, perhaps, a small amount C84+ (less-than-or-equal-to 1.5%) ions are observed. As the fluence is increased, fragmentation of these species and aggregation to larger clusters are observed. Post-ionisation of neutral desorbed species with 248 or 308 nm is much less efficient and leads to substantial fragmentation both immediately on ionisation as well as in the field-free region of the mass spectrometer (a timescale of up to 100-mu-s).