Multiply negatively charged aluminium clusters
The first observation of gas-phase aluminium dianions, Aln2-, is reported. Singly negatively charged aluminium clusters are converted to dianions by exposure to low-energy electrons in a Penning trap. Attachment of such secondary electrons to the monoanions leads to the formation of dianionic clusters, as earlier observed for the noble metals, copper, silver and gold. The present work extends the `electron-bath technique' to the trivalent aluminium. The observation of Aln2- as a function of cluster size is compared to estimates of the second electron affinities of Aln as given by a combination of first electron affinities and the charged conducting-sphere model. This simple approach is found to describe the appearance size (size of smallest Aln2- observed) very well.
PACS.36.40.-c Atomic and molecular clusters 36.40.Wa Charged clusters
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