MIXED SILICON-CARBON DIANIONS AND THEIR STABILITY IN THE GAS-PHASE

Free dianionic mixed silicon-carbon clusters SixCy2- (x=1,2 y=4-9) hav e been studied by standard ab initio methods. Branched, chainlike, and cyclic isomers have been investigated in detail. The smallest system that has been found to be clearly stable with respect to electron auto detachment and fragmentation is a triangular seven atomic SiC62- diani on, better referred to as Si(C-2)(3)(2-)(.) Chainlike isomers are less stable than the corresponding branched isomers. The onset of electron ic stability within the chainlike structural class is predicted to occ ur at the eight atomic cluster dianion Si2C62-. Small stable cyclic is omers have not been found. The bonding mechanisms of the excess electr ons in the different isomers are discussed and the systems are compare d with other small gas-phase dianions. Furthermore, the essentially di fferent principles of building up dianionic, monoanionic, and neutral mixed silicon-carbon clusters are explained and discussed. (C) 1998 Am erican Institute of Physics.