The structures and abundances of C-n=2-16(+) clusters produced by electronic sputtering from the impact of Cf-252 fission fragments on CO ice and from the UV laser desorption of amorphous carbon and graphite targets are analyzed. A systematic search for the more stable conformers at the DFT/B3LYP level of calculation and their contribution to the mass spectra is reported. A new methodology for a proper taxonomic description of the cluster isomers is proposed. Besides the known linear and monocyclic clusters series, new members of these series and two new series are described: the bi-cyclic and/or tri-cyclic and the rhombic core series. (c) 2006 Elsevier B.V. All rights reserved.