Theoretical study of electron capture dissociation of [Mg(H2O)n]2+ clusters

The electron capture dissociation (ECD) of [Mg(H2O)n]2+ clusters is examined using ab initio electronic structure methods to interpret experimental data on [Mg(H2O)n]2+ and [Ca(H2O)n]2+. Calculations are performed on Mg2+(H2O)n clusters containing a full first hydration shell plus one or two additional water molecules positioned to represent second- and third-shell molecules. The propensity of the Mg-containing clusters to undergo fragmentation primarily into [Mg(H2O)n−m]1+ + m H2O (m = 10) for n > 17 but primarily into [Mg(OH)(H2O)n−k]1+ + H + (k−1) H2O (k−1 = 10) for n < 17 (for Ca-containing clusters, the transition occurs near n = 22) is rationalized in terms of a model in which: