Double photoionization of C₆₀ and C₇₀ in the valence region

The photoion yields for production of C²⁺₆₀ and C²⁺₇₀ were measured in the Hv range from 25 to 150 eV. The photon flux of the synchrotron radiation was estimated by measuring the photocurrent from a silicon photodiode. The fullerene ions produced in the interaction region were extracted by a pulsed electric field and mass-separated by a time-of-flight mass spectrometer. The yield ratios of of the ions were found to be larger than unity at hv>50 eV. This suggests that the slightly charged ions produced by the spectator Auger ionization rapidly emit another electron to form C²⁺₆₀ or C²⁺₇₀.