FORMATION OF SILICON-CARBIDE CLUSTER CATIONS AND THEIR REACTION WITH ACETYLENE - UNUSUAL BEHAVIOR OF THE DISILICON CARBIDE IONS

Formation of silicon carbide cation clusters (SiC(y)+, y = 0-12 and Si2Cy+, y = 0-11) by direct laser vaporization is reported. The reactions with acetylene were studied in a Fourier transform ion cyclotron resonance mass spectrometer, and product branching ratios and rate constants are tabulated. Monosilicon carbide cations react similarly to pure carbon clusters to add C2H at a rate approximately half Langevin. These results are interpreted as favoring a linear Si-C(y)+ structure possessing a reactive carbene site. Disilicon carbide cations exhibit unusual non-linear kinetics: at first reacting slowly to add CH2, followed by an increase in reactivity and adduct formation. Carbon-13 labeling studies reveal that the Si2Cy+ (y > l) reactant ions undergo carbon exchange with acetylene, catalyzing cleavage of the carbon-carbon triple bond!