Lanthanide Oxide Cluster Ions Generated by Vacuum Laser Ablation: Metal Valence Effects on Cluster Compositions

Abstract

Pulsed XeCl excimer laser ablation ([gamma] = 308 nm; irradiance approximately 10 MW cm[sup [minus]2]) of hydrated lanthanide oxalates into vacuum has been found to generate significant yields of lanthanide oxide cluster ions, the compositions of which were analyzed by reflection time-of-flight mass spectrometry. Cluster ions, Ln[sub m]O[sup +][sub n], were identified for all of the lanthanides studied: Ln = Sm, Eu, Gd, Tb, and Yb. In each case, ions with metal contents (m) of up to at least 26 were detected, with the largest cluster identified being Tb[sub 63]O[sub 94][sup +] (mass = 11 516 amu). A distinctive sequence of cluster compositions was found for each Ln, apparently reflecting the relative accessibilities of the +2, +3, and +4 oxidation states. On the basis of the observed cluster stoichiometry distributions, it was concluded that trivalent metal sites were dominant in each series of Ln[sub m]O[sup +][sub n]. However, cluster ions were identified for Sm and Gd. A double-chain polymeric lanthanide oxide schematic structure is postulated to provide a coherent picture of the observed clustering behaviors. 40 refs., 9 figs., 4 tabs.