Stability, kinetics, and magic numbers of Si+n (n=7–45) clusters

Mass spectrum maxima of Si+n clusters recently measured by Bloomfield, Freeman, and Brown are discussed in terms of cluster geometries they inferred from photofragmentation branching ratios and additional geometries proposed here. Critical slowing of cluster formation kinetics for n near 10 is explained by a configuration coordinate model. The critical slowing arises from the same factors thought to be responsible for network glass formation in bulk. Specifically, Si+n can be described as the smallest ‘‘glass’’ cluster known.