Abstract
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.