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 [O2·(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 [O2·(H2O)n]+ clusters [J. Phys. Chem. A 103 (1999) 2999].