Sequential Reactions of Bare Silicon Clusters with SiD sub 4: Constrained Heterogeneous Nucleation of Hydrogenated Silicon Particles.

Bare silicon cluster ions are observed to undergo exothermic sequential clustering reactions with SiD sub 4 at room temperature. Si sup + sub (1-7) and Si sup - sub (1-7) are created by laser evaporation and trapped in the ion cell of a Fourier transform mass spectrometer in the presence of SiD sub 4. These clustering reactions are observed only for Si sup + sub (1-3) and Si sup + sub 5. Si sup + sub (4,6,7) and the negatively charged silicon clusters do not react exothermically with SiD sub 4. All of the reactive silicon clusters encounter chemical constraints to rapid growth of increasingly larger Si sub x H sup + sub y species. Ab initio electronic structure calculations are used in concert with phase space theorectical calculations to deduce the structures of the products of the clustering reactions. These structures are found to be closely related to the lowest energy structures of the bare clusters if the degree of hydrogen saturation is low.