MULTIPHOTON IONIZATION AND FRAGMENTATION OF TRANSITION-METAL CLUSTER OXIDES - HIGH-TEMPERATURE METAL-OXIDE COMPOSITIONS

Clusters of vanadium, chromium, nickel, and iron oxide are prepared by oxidation of the corresponding metal clusters in a flow-tube reactor. The cluster oxides are detected by multiphoton ionization and time-of-flight mass spectrometry. The observed oxide ion compositions rapidly assume a constant oxygen-to-metal ratio with increasing cluster size, and these compositions appear to correspond to high-temperature congruently vaporizing species in the metal-oxygen phase diagrams. Although cluster heating occurs in the flow tube as a consequence of the exothermicity of the oxidation reaction, the final ionic species that are seen most likely reflect the high temperatures produced in the multiphoton ionization process that is accompanied by extensive cluster fragmentation.