The ionic KAl13 molecule: a stepping stone to cluster-assembled materials.

Theoretical calculations by Khanna and Jena predicted KAl(13) to be an ionically bonded, cluster-assembled "diatomic molecule," i.e., K(+)Al(13) (-). We have conducted both mass spectral and anion photoelectron spectroscopic studies on KAl(n) (-), finding a "dip" at n=13 in both their mass spectrum and in their electron affinity versus n trend. While these largely qualitative results are consistent with KAl(13) being a salt, they can also be explained in terms of the shell model and thus, by themselves, are not conclusive. Quantitative comparisons between calculated photodetachment transition energies and the photoelectron spectrum of KAl(13) (-), however, allow a strong case to be made for ionic bonding in KAl(13). As a prototype for ionic bonding involving intact Al(13) (-) subunits, KAl(13) may be a stepping stone toward forming ionic, cluster-assembled materials.