Ionization energies and structures of small lanthanum oxide clusters (La2O3)n.LaO (n=1-3)

Small lanthanum oxide clusters were produced in a laser-ablation molecular beam setup and studied by mass spectrometry and laser threshold photoionization spectroscopy. Mass spectrometry investigations of neutral clusters revealed certain stoichiometries, (La2O3)(n) and (La2O3)(n).LaO (n = 1-6) were stable. For cation clusters, similar stoichiometric preference was reported by previous authors. The stoichiometric preference of the oxides was not affected by oxygen concentrations. Ionization thresholds and vertical ionization energies (VIEs) were measured for the (La2O3)(n).LaO (n = 1-3) neutral clusters from the photoionization efficiency curves. The energetically low-lying structural isomers for these clusters along with their adiabatic and vertical ionization energies were computed from the density functional theory using B3LYP and PW91GGA exchange correlation functionals. Favorable agreement between the computed and experimental ionization energies allows assignments of the ground state structures for these clusters. For La3O4, a C-3v-like structure has been found as the ground state built on La-O-La bonds with their usual oxidation states of +3 for La and -2 for O atoms. For larger clusters La5O7 and La-7 O-10, however, a trend towards forming more compact structures with few metal and O sites having higher coordination numbers have been found as the ground states and are suggested to be present in the molecular beam.