Dissociation patterns of (H2O)n+ cluster ions, for n=2-6

Metastable and collision-induced fragmentation patterns have been recorded for size-selected (H2O)(n)(+) cluster ions, where n = 2-6. The results show evidence of a competitive loss of OH and H2O from each of the ions; however, as the size of the parent ion increases there is a corresponding increase in the relative loss of H2O from each cluster. This behaviour is interpreted as the predominant formation of an H3O+-OH central core with additional H2O ligands present in the first solvation shell. The results are discussed with reference to the chemistry of the ionosphere, where [O-2 . (H2O)(n)](+) intermediates are thought to contribute to the formation of proton hydrates, H+(H2O)(n). However, recent laboratory measurements have shown that (H2O)(n)(+) ions are the main fragmentation products from [O-2 . (H2O)(n)](+) clusters [J. Phys. Chem. A 103 (1999) 2999]. (C) 2001 Elsevier Science B.V. All rights reserved.