SWITCHING REACTIONS ON AND OFF IN NO-CONTAINING CLUSTER IONS EVIDENCEOF CHEMICAL PROCESSES THAT ARE PROBABLY UNIQUE TO SYSTEMS OF A FINITE-SIZE

Presented here are the results of a series of experiments where the fr agmentation patterns of the cluster ions (CH3OH)n.NO+, (CH3OH)n.(H2O)m .NO+, (CH3COCH3)n.NO+, and (CH3COCH3)n.(H2O)m.NO+ have been monitored as a function of n and m. At certain critical values of n and/or m, th e ions lose XNO, where X is either HO or CH3O and, for those clusters containing three distinct chemical species, precise combinations of n and m lead to specific reactions being either 'switched-on' or 'switch ed-off'. In most cases, these reactions require a minimum of four mole cules to be present in a cluster; however, there are examples of five- and six-body processes involving three separate chemical species. Giv en these rather restricted constraints on size and composition, it is proposed that some of the observed chemical processes could only proce ed within the confines of a gas-phase cluster.