3 STRUCTURAL TYPES OF CARBON CLUSTER ANIONS AND THE MAGIC NUMBERS

The distribution of negative carbon clusters, C(n)-, is studied in the size range from 4 to 100 atoms using a Smalley compact supersonic source interfaced to a Fourier transform mass spectrometer. The mass spectrum of the anion clusters shows three regions which, based on earlier work, can be assigned to three different types of structures: chain, monocyclic and fullerene. The boundaries observed for the three regions in the mass spectrum suggest that the transition from chain to cyclic structure occurs between C33- and C14-, and the one from cyclic structure to fullerene occurs in the region of C33- to C59-. Magic numbers in the cyclic cluster region are found to be 17, 21, 25, 29 and 33 (n = 4m + 1), and in the fullerene region, 60 and 74. Water can react with carbon clusters in the supersonic source to form hydrogenation products followed by electron attachment to give C(n)H- and C(n)H2- (for even n smaller than about 22). With argon as the target gas, only small C(n)- (n < 14, except n = 4) are observed to undergo low energy collision-induced dissociation (CID) yielding mainly C(n-3)-. While CID of C(n)H- gives C(n)-, no product was observed during CID of C(n)H2-.