Ion−Molecule Reactions of Gas-Phase Chromium Oxyanions:  Cr x O y H z - + H2O

Chromium oxyanions having the general formula Cr x O y H z - play a key role in many industrial, environmental, and analytical processes, which motivated investigations of their intrinsic reactivity. Reactions with water are perhaps the most significant, and were studied by generating Cr x O y H z - in the gas phase using a quadrupole ion trap secondary ion mass spectrometer. Of the ions in the Cr1O y H z envelope (y = 2, 3, 4; z = 0, 1), only CrO2 - was observed to react with H2O, producing the hydrated CrO3H2 - at a slow rate (∼0.07% of the ion−molecule collision constant at 310 K). CrO3 -, CrO4 -, and CrO4H- were unreactive. In contrast, Cr2O4 -, Cr2O5 -, and Cr2O5H2 - displayed a considerable tendency to react with H2O. Cr2O4 - underwent sequential reactions with H2O, initially producing Cr2O5H2 - at a rate that was ∼7% efficient. Cr2O5H2 - then reacted with a second H2O by addition to form Cr2O6H4 - (1.8% efficient) and by OH abstraction to form Cr2O6H3 - (0.6% efficient). The reactions of Cr2O5 - were similar to those of Cr2O5H2 -: Cr2O5 - underwent addition to form Cr2O6H2 - (3% efficient) and OH abstraction to form Cr2O6H- (