Carbon clusters in a storage ring

Anions of fullerenes and small carbon clusters C-n(-) have been stored in the storage ring ASTRID and observed served decays on a millisecond time scale are interpreted as electron emission from metastable excited states. For the fullerenes, the fast decay is caused by thermionic emission, quenched by radiative cooling. The observed decay times are longest for the magic numbers n = 50,60, reflecting a reduction of the thermal radiation due to the electronic shell structure. This statistical interpretation is supported by experiments on thermionic emission from C-60(-) molecules heated by a Nd:YAG laser pulse. For anions of small carbon clusters (n = 2 - 9) there is a metastable component for n = 2 and for odd n but no metastability on a millisecond time scale for even n. The excited states are suggested to be quartet states decaying by Auger emission.