Reactivity of Size-Selected Silicon Clusters As Studied By Fourier Transform Mass Spectrometry.

The chemistry of positively and negatively charged bare silicon cluster ions is investigated using laser evaporation coupled with Fourier transform ion cyclotron resonance mass spectrometry. Systematic trends in the rates and products with cluster size indicate that small ionic silicon clusters have two distinct types of reactivity. These two types are related to different dangling bonds of the clusters involving either a divalent or a trivalent (or charged) silicon center. This interpretation agrees well with ab initio electronic structure calculations as well as known reactivity of divalent and radical organosilicon centers. "Magic numbers" and reaction thermodynamics are of little heuristic value in explaining these trends in the reaction rates and product distributions. This is a review of our recent work on the chemistry of size-selected silicon cluster ions and will be published in the NATO ASI series as part of a compendium of papers given at the International Symposium on the Physics and Chemistry of Small Clusters.