Experimental verification of the high stability of Al H:13 a building block of a new type of cluster material?

y Photoelectron spectra of mass-separated, negatively charged, bare and reacted aluminium clusters Al H ns12–14,n m.ms0–2 are presented and compared to the results of corresponding calculations. A large HOMO–LUMO gap of 1.4 eV is found for the neutral Al H cluster, indicating an extraordinarily high stability of this cluster. Adsorption of a second13 hydrogen atom results in the disappearance of the gap. Since the discovery of fullerenes a new dimension has been added to cluster science: the search for new materials consisting of clusters. However, such mate-rials are metastable and they can only exist, if there is a barrier for reactions with identical clusters and with the substances used in the processes of extrac-tion and separation. Few cluster materials are known at present. Most famous are the various new materi-w xals consisting of fullerenes like C and C 1.60 70 These clusters are closed-shell species with a rela-tively large HOMO–LUMO gap HOMO: highest occupied molecular orbital, LUMO: lowest unoccu-.pied molecular orbital. The most stable species C60 has a HOMO–LUMO gap of 1.7 eV, while the gap w xfor the less stable C is;1.0 eV 2,3. Generally,7