CO/O Exchange in Magnesium-Water Clusters Mg(HO) .

Hydrated singly charged metal ions doped with carbon dioxide, Mg(CO)(HO) , in the gas phase are valuable model systems for the electrochemical activation of CO. Here, we study these systems by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry combined with ab initio calculations. We show that the exchange reaction of CO with O proceeds fast with bare Mg(CO), with a rate coefficient k = 1.2 × 10 cm s, while hydrated species exhibit a lower rate in the range of k = (1.2-2.4) × 10 cm s for this strongly exothermic reaction. Water makes the exchange reaction more exothermic but, at the same time, considerably slower. The results are rationalized with a need for proper orientation of the reactants in the hydrated system, with formation of a Mg(CO)(HO) intermediate while the activation energy is negligible. According to our nanocalorimetric analysis, the exchange reaction of the hydrated ion is exothermic by -1.7 ± 0.5 eV, in agreement with quantum chemical calculations.