Desorption of Oxygen from Cationic Niobium Oxide Clusters Revealed by Gas Phase Thermal Desorption Spectrometry and Density Functional Theory Calculations.

Thermal dissociation of cationic niobium oxide clusters (NbO) was investigated by gas phase thermal desorption spectrometry. The dominant species formed at 300 K were NbO (n = 2, 4, 6, ...; p = 0, 1, 2, ...) and NbO (n = 3, 5, ...; q = 0, 1, 2, ...). At higher temperatures, the more oxygen-rich clusters were observed to release O. However, the desorption of O from NbO was found to be insignificant in comparison with VO because Nb tends to have a +5 oxidation state exclusively, whereas V can have both +4 and +5 oxidation states. The propensity for the release of O atoms was manifested in the formation of NbO from NbO for odd values of n, whereas VO released O molecules instead. The energetics of the O and O release from the Nb and V oxide clusters, respectively, was consistent with the results of DFT calculations.