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.
Thermal dissociation of the cationic niobium-vanadium oxide clusters, NbVO (n + m = 2-8), was investigated by gas phase thermal desorption spectrometry. The oxygen-rich NbVO released O and O for odd and even values of n + m, respectively. Substitution of more than one Nb atom in NbO by V drastically lowered the desorption temperature of O for even values of n + m, whereas the substitution of more than two Nb atoms opened a new desorption path involving the release of O for odd values of n + m. The substitution effects can be explained by the fact that Nb atoms display the +5 state, whereas V atoms can exist in either the +4 or +5 states. The geometrical structures of selected NbVO clusters were optimized and the energetics of the release of O/O from the clusters was discussed on the basis of the results of DFT calculations.
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