Combined experimental and theoretical study of small aluminum oxygen clusters

We report a combined experimental and computational investigation of small AlnOm species (n <= 20, m <= 12), produced in a laser vaporization cluster source. The oxygen content in the clusters was tuned by varying the oxygen concentration in the carrier gas. Ionization energies are bracketed using different ionizing photon energies in the energy range between 5.37 and 7.89 eV. Among the singly doped AlnO species, Al3O and Al15O are found to have relatively low ionization energies, which can be related to the magic character of the corresponding cations. Peculiarly low ionization energies also are observed for specific oxygen rich species (m > 1), suggesting the formation of ionically bound subunits. The structures and ionization energies of singly doped AlnO0,+ (n = 1-7) clusters were determined using density functional theory (B3LYP/6-311+G(d)).