Stability and reactivity of hydrated magnesium cations

Unimolecular fragmentation and bimolecular reactions with HCl of water clus ters which nominally contain Mg+ cations were studied in an FT-ICR spectrom eter. A cluster fragmentation and successive evaporation of single water mo lecules occurring on a millisecond timescale and driven by ambient black bo dy radiation is triggering interesting intracluster reactions. Below a cert ain critical size (similar to 17 water molecules) MgOH+ forms, and a hydrog en atom is ejected. Similarly bimolecular reactions of Mg-aq(+) clusters wi th HCl result in a release of H atom and formation of MgClaq+. Both finding s can be rationalized by assuming that the solvated Mg+ cations actually de tach an additional electron forming a Mg-aq(2+) and e(aq)(-) within cluster s with more than 17 water molecules. Mg+ formed by recombination when not e nough solvent is available to stabilize the separate charged species then r eacts with a water molecule resulting in H-atom formation. Detailed studies of the ion reactions and fragmentation provide additional insights into th e structure and stability of solvated magnesium cations. (C) 1998 Elsevier Science B.V. All rights reserved.