Termination of the W(2)O(y) (-)+H(2)O/D(2)O-->W(2)O(y+1) (-)+H(2)/D(2) sequential oxidation reaction: An exploration of kinetic versus thermodynamic effects.

Several mechanisms proposed and calculated for the sequential oxidation of tungsten suboxide clusters by H(2)O/D(2)O [Mayhall et al., J. Chem. Phys. 131, 144302 (2009)] are evaluated using anion photoelectron spectroscopy of an apparent intermediate, W(2)O(6)D(2) (-). The spectrum of W(2)O(6)D(2) (-) is consistent with the W(2)O(5) (-)+D(2)O-->W(2)O(6) (-)+D(2) intermediate in which the initial water addition involves the interaction of the oxygen from D(2)O with a tungsten atom, approaching from a direction with the least repulsion from the W(2)O(5) (-) oxygen atoms, coupled with the interaction between a deuterium with a tungsten-tungsten bridging oxygen on the cluster. The presence of W(2)O(6)H(2) (-) and W(2)O(6)D(2) (-) suggests that there is insufficient internal energy in the complex to surmount the barrier for rearrangement required for tungsten hydride and hydroxide formation necessary for H(2) or D(2) evolution, which was calculated to be energetically favorable. The quality of the calculations is verified by direct comparison between experimental photoelectron spectra of W(2)O(5) (-) and W(2)O(6) (-) and spectral simulations generated from the lowest energy structures calculated for W(2)O(5) (-), W(2)O(6) (-) and their corresponding neutrals. The results shed light on the importance of repulsion on the pathway a reaction follows under room temperature conditions.