SMALL DIANIONIC CARBON CLUSTERS - GENERAL-ASPECTS ON THEIR STABILITY AND RESULTS FOR C-9(2-)

Studies on several geometrical configurations of the free doubly negat ive carbon cluster C-9(2-) are performed at the Hartree-Fock level as well as at the configuration interaction and outer-valence Green's fun ction levels of theory. Most of the C-9(2-) isomers inspected are foun d to be stable with respect to fragmentation, but only two structures, a branched cluster and a D-3h symmetrical isomer, emerge also as stab le with respect to electron autoejection. The characteristic propertie s which allow small free dianionic carbon clusters to bind two excess electrons are discussed. Qualitative structural criteria for the exist ence of these cluster dianions are extracted by comparing and generali zing the results for C-7(2-), C-8(2-), C-9(2-), and C-10(2-). Predicti ons of possible structures of stable higher carbon cluster dianions ar e made.