CO(2)/O(2) Exchange in Magnesium–Water Clusters Mg(+)(H(2)O)(n)

[Image: see text] Hydrated singly charged metal ions doped with carbon dioxide, Mg(2+)(CO(2))(−)(H(2)O)(n), in the gas phase are valuable model systems for the electrochemical activation of CO(2). 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(2) with O(2) proceeds fast with bare Mg(+)(CO(2)), with a rate coefficient k(abs) = 1.2 × 10(–10) cm(3) s(–1), while hydrated species exhibit a lower rate in the range of k(abs) = (1.2–2.4) × 10(–11) cm(3) s(–1) 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(2+)(CO(4))(−)(H(2)O)(n) 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.