Eur. Phys. J. D (2013) 67: 39
https://doi.org/10.1140/epjd/e2012-30265-3

Regular Article

Appearance size of poly-anionic aluminum clusters, Al_n^z-, z = 2–5^*

Institut für Physik, Ernst-Moritz-Arndt-Universität, 17487 Greifswald, Germany

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Received: 21 April 2012
Received in final form: 20 November 2012
Published online: 6 March 2013

Abstract

The production of poly-anionic metal clusters by simultaneous storage of electrons and cluster anions in a Penning trap has been extended to the fifth charge state. The minimum cluster size, required to attach a fifth excess electron, has been experimentally determined for aluminum clusters. A refined data evaluation method is proposed, redefining the appearance size with respect to the delayed electron emission. It has been applied to the penta-anions as well as to previous data of poly-anionic aluminum clusters. In addition, new measurements of aluminum di-anions have revealed a lower minimum appearance size than reported earlier. Comparison of the experimental results with predictions by the conducting-sphere model for the di-, tri-, tetra- and penta-anions show deviations that are probably due to thermal excitation of the cluster anions. The cluster-size dependence of the poly-anion abundance spectra is qualitatively reproduced by thermionic emission.