Reactive nucleation of silver clusters with oxygen and water

The nucleation of silver atoms by the gas aggregation technique when adding O-2 and H2O molecules in the carrier gas was investigated by photoionization mass spectrometry. No change appeared in the bare silver cluster mass spectra when only water was added to the nucleation carrier gas. In the presence of oxygen and water, reactive nucleation occurred simultaneously. At low reactive gas concentration (unsaturated regime), AgnOxHy compounds with x = 2, 3 and 4 are produced for n greater than or equal to 6. For a larger reactive gas concentration (saturated regime) two series of cluster bunches having Ag3O3Hy as the building block were observed. The precursors of these series are (Ag4O3Hy)(+) and (Ag5O5Hy)(+), respectively. This behavior differs totally from the results obtained for reactive nucleation of an alkaline vapor but can be viewed as a precursor of the surface silver hydroxidation mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.