Electron emission from laser-heated fullerene dianions: Probing the repulsive Coulomb barrier

Electron detachment from fullerene dianions Cm2- (m=76,84) stored in a room temperature Penning trap was probed upon pulsed laser excitation at wavelengths of 355 and 532 nm. The fraction of Cm(2-) surviving trapping times exceeding tens of milliseconds under UHV conditions, as well as the fraction of singly charged anions Cm(-) generated were recorded as a function of the laser fluence. Analysis by means of Poisson statistics yields absolute absorption cross sections and the number of photons necessary to induce the detachment. The cross sections obtained are in good agreement with the literature values. By describing the electron detachment as a statistical unimolecular process, we deduce effective activation energies from the number of photons required. These energies are compared to the sum of the second electron affinity and the Coulomb barrier height as calculated from an electrostatic charging model.