On the generation and stability of isolated doubly negatively charged fullerenes

Intense fullerene anion beams were generated by electrospray of dichlorobenzene solutions of fullerenes and tetrakis(dimethylamino)ethylene (TDAE). Ions were probed with Fourier transform mass spectrometry (FTMS) about one second after the electrospray step. In addition to monoanions, large quantities of fullerene dianions were detected. The efficiency of dianion formation and detection was found to increase dramatically with cage size. While C602− could not be observed, dianions of trace fullerenes up to C1242− were readily accessed. Among all fullerene dianions probed only C702− was found to be metastable under collision-free conditions on the measurement timescale with a half-life of about 80 s towards electron autodetachment. Observation and stability of fullerene dianions are discussed in terms of rough estimates of their second electron affinities.