Formation of silicon carbide cluster cations and their reaction with acetylene. Unusual behavior of the disilicon carbide ions

Abstract

Formation of silicon carbide cation clusters (SiC + y , y = 0–12 and Si 2C + y , 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 C 2H 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 CH 2, followed by an increase in reactivity and adduct formation. Carbon-13 labeling studies reveal that the Si 2C + y ( y > 1) reactant ions undergo carbon exchange with acetylene, catalyzing cleavage of the carbon-carbon triple bond!