ADHESION OF AGI MOLECULES TO GASEOUS METALLIC SILVER CLUSTER CATIONS

The evaporative channels for the unimolecular dissociation of metastable Ag(X)I(Y)+ (X = 5-25; Y = 0-4) clusters made by fast atom bombardment of silver foil in the presence of CH3I vapor are observed in the first field-free region of a double-focusing mass spectrometer. We found three dominant neutral evaPorative channels: Ag loss, Ag2 loss, and AgI loss. Only Ag12I3+ is found to have an additional channel involving an (AgI)3 loss. Consistent with our previous studies of stable Ag(X)I(Y)+ clusters, we assume a structural formula of (Ag(X-Y))+(AgI)Y, where the metallic part of the cluster conforms to Jellium model predictions. In comparing the relative evaporative loss of AgI from these metastable clusters, we observe: (a) evidence for significant AgI-AgI interaction for clusters whose metallic part has a 1s2, 1p2, or 1s(2)1p4 Jellium configuration; (b) a near constant fractional loss of AgI as the number of AgI units in the parent cluster increases for clusters whose metallic part has a closed main Jellium shell; (c) a relative increase in the fraction loss of AgI as the number of AgI molecules in the parent cluster increases for clusters with an ''open''-shell configuration for the metallic part. These observations are discussed in terms of evaporative loss of AgI from structures in which the AgI molecules solvate the metallic part of the cluster. It is proposed that the heat of AgI evaporation is greatly determined by dipole/induced-dipole interactions between the permanent dipole of AgI and the polarizable delocalized electron density of the metallic part of the cluster.