Metastable fragmentation of silver bromide clusters |
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Authors: | J.-M. L'Hermite F. Rabilloud L. Marcou P. Labastie |
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Affiliation: | (1) Laboratoire CAR/IRSAMC, Université Paul Sabatier, 118 route de Narbonne, 30062 Toulouse Cedex, France, FR |
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Abstract: | The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most abundant species are AgnBrn - 1 + and AgnBrn + 1 - and Ag14Br13 + is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide ionic clusters. From a certain size, AgnBrn - 1 + is no more the main series, and AgnBr n - 2, 3 + series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental method. The large majority of the cations release mainly a neutral Ag3Br3 cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag+-Ag+ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)3 and to quasi-planar cyclic structures of (AgBr)n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)n, and to cuprous halide compounds. Received 9 November 2000 and Received in final form 25 January 2001 |
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Keywords: | PACS. 36.40.Qv Stability and fragmentation of clusters |
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