Stability and reactivity of hydrated magnesium cations

Unimolecular fragmentation and bimolecular reactions with HCl of water clusters which nominally contain Mg+ cations were studied in an FT-ICR spectrometer. A cluster fragmentation and successive evaporation of single water molecules occurring on a millisecond timescale and driven by ambient black body radiation is triggering interesting intracluster reactions. Below a certain critical size (similar to 17 water molecules) MgOH+ forms, and a hydrogen atom is ejected. Similarly bimolecular reactions of Mg-aq(+) clusters with HCl result in a release of H atom and formation of MgClaq+. Both findings can be rationalized by assuming that the solvated Mg+ cations actually detach an additional electron forming a Mg-aq(2+) and e(aq)(-) within clusters with more than 17 water molecules. Mg+ formed by recombination when not enough solvent is available to stabilize the separate charged species then reacts with a water molecule resulting in H-atom formation. Detailed studies of the ion reactions and fragmentation provide additional insights into the structure and stability of solvated magnesium cations. (C) 1998 Elsevier Science B.V. All rights reserved.