FORMATION OF ELECTRONICALLY EXCITED AGXO FROM THE OXIDATION OF SMALL SILVER CLUSTERS

The chemiluminescent reactions of silver clusters, Mn, n ≥ 3, with ozone have been studied under multiple-collision conditions. As a function of variations in the silver flux, a minimum of five distinct electronic emissions associated with AgO, AgxO (x ∼ 2), and Ag2 are observed as well as features that are tentatively associated with the higher silver cluster oxides. The energetics of the observed spectral features combined with supplementary thermodynamic and kinetic information demonstrate that it is unlikely that electronically excited products with enough energy to account for the observed chemiluminescence can be produced through the reaction of either Ag or Ag2 with O3. The smallest cluster whose reactions can readily yield the observed AgO emission features is the trimer. The formation of Ag2O* can also be achieved through reaction of the trimer; however, it may better be accounted for via the reaction of higher clusters. At moderate silver fluxes, the observed chemiluminescence is dominated by the AgO A2Π-X2Π (400-420 nm) and B2Π-X2Π (320-370 nm) emission features. At higher silver fluxes, leading to greater agglomeration, both the AgO A-X and B-X emissions are quenched and the spectrum is dominated by a combination of AgxO (x ∼ 2) and Ag2 emission features extending from 420 to 700 nm. At even higher silver flux further spectral features at λ > 680 nm emerge. The chemiluminescent spectrum between 500 and 700 nm has been found to contain two distinct emission band regions which have been assigned as the A-X and B-X band systems of Ag2O. The A-X transition which onsets at ∼630 nm is well fit by the expression v (cm-1) = 15670 - 165v2″ + 0.4(v2″)2. The B-X transition which originates at 506 nm is well fit by the expression vv1Prime;,v2″,v3″ (cm-1) = 19766 - 442v1″ - 165v2″ - 256v3″ + 6(v1″)2 + 6v1″v3″ + 25v1″v2″. The observed frequencies are consistent with a nonlinear Ag-Ag-O structure, emission from the asymmetric cluster oxides characterizing these kinetically controlled oxidation experiments in contrast to the thermodynamically more stable symmetric species. © 1990 American Chemical Society.