Unusual products observed in gas-phase Wx O_y^- + H₂ O and D₂ O reactions

Addition of H₂ O and D₂ O to small tungsten suboxide cluster anions Wx O_y^- (x=1-4; y3x) was studied using mass spectrometric measurements from a high-pressure fast flow reactor. Within the WO y- mass manifold, which also includes WO₄ H-, product masses correspond to the addition of one to three H₂ O or D₂ O molecules. Within the W₂ O_y^- cluster series, product distributions suggest that sequential oxidation W₂ O _y^- + H₂ O/ D₂ O→ W₂ O y+1 - + H₂ / D₂ occurs for y<5, while for W ₂ O₅-, W₂ O₆ H₂- / W ₂ O₆ D₂- is primarily produced. W₂ O₆- does not appear reactive. For the W₃ O _y^- cluster series, sequential oxidation with H₂ and D₂ production occurs for y<6, while W₃ O ₆- and W₃ O₇- produce W₃ O ₇ H₂- / W₃ O₇ D₂- and W₃ O₈ H₂- / W₃ O₈ D ₂-, respectively. Lower mass resolution in the W₄ O _y^- mass range prevents definitive product assignments, but intensity patterns suggest that sequential oxidation with H₂ / D₂ evolution occurs for y<6, while W₄ O_y+1 H₂- / W₄ O_y+1 D₂- products result from addition to W₄ O₆- and W₄ O₇-. Based on bond energy arguments, the H₂ / D₂ loss reaction is energetically favored if the new O- Wx O_y^- bond energy is greater than 5.1 eV. The relative magnitude of the rate constants for sequential oxidation and H₂ O/ D₂ O addition for the x=2 series was determined. There are no discernable differences in rate constants for reactions with H₂ O or D₂ O, suggesting that the H₂ and D₂ loss from the lower-oxide/hydroxide intermediates is very fast relative to the addition of H₂ O or D ₂ O.