Excimer laser (X = 308 nm) ablation of solid Yb2O3 into vacuum has been found to generate polyatomic ytterbium oxide ions : Yb-2(+), Yb2O+, Yb2O2+, Yb304+, and Yb6O8+. In contrast, other Ln(2)O(3) (Ln = Sm, Eu, Gd, Dy) formed observable amounts of only the atomic and/or monoxide ions, Ln(+) and LnO(+). The stoichiometry of Yb6O8+ suggests mixed-valence Yb-II/III content. The vapor composition found for vacuum ablation of Yb2O3 differs notably from both that reported for equilibrium vaporization of Yb2O3 and that for reactive (with O-2) condensation of ablated ytterbium metal.