Mg+(H2O)n clusters ions are known to undergo a hydrogen loss reaction to produce (MgOH)+(H2O)n−1, when the cluster size n falls between 5 and 15. It indicates that the microscopic solvation environment has a strong effect on the reaction mechanisms, which have now been elucidated. Above n
= 6, Mg+(H2O)n exists in the form of an ion pair, Mg2+(H2O)l⋯e−(H2O)n−l, and H+ is produced by the autoionization of H2O, enhanced by the hydrolysis of Mg2+. Production of the H atom is due to a reductive half reaction H+
+ e → H, with the electron being the solvated electron in the ion pair. The reaction barrier is reduced when the electron is in the first or second solvation shell, promoting the H loss reaction. As the number of H2O molecules increases, the electron moves beyond the third solvation shell and the reaction barrier increases significantly, which is responsible for the subsequent switch-off of H loss. It has been one of the important goals in cluster sciences to understand the microscopic correlation between solvation and chemical reactivity by in-depth study on clusters, which has now been achieved in the case of Mg+(H2O)n, linking electron solvation with reaction paths for electron transfer.
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