AlH₃ and Al₂H₆: Magic Clusters with Unmagical Properties

Enhanced stability, low electron affinity, and high ionization potential are the hallmarks of a “magic” cluster. With an electron affinity of 0.28 eV, ionization potential of 11.43 eV, and a large binding energy, AlH₃ satisfies these criteria. However, unlike other magic clusters that interact only weakly with each other, two AlH₃ clusters bind to each other with an energy of 1.54 eV. The resulting Al₂H₆, while also a magic cluster in its own right, possesses the most unusual property that the difference between its adiabatic and vertical detachment energy is about 2 eV—the largest of any known cluster. These results, based on density functional theory, are verified experimentally through photodetachment spectroscopy.