Evidence for trimers evaporation in silver bromide clusters

Metastable fragmentation channels of free silver bromide clusters (AgnBrp)(+) are reported. The large majority release a neutral trimer (AgBr)(3). This is interpreted in the frame of ab initio DFT calculations with 19-electron pseudopotential on silver atom. The stability, the structural and electronic properties of (AgnBrp)((+)) (n = 6, p = n, n - 1) are examined. The structures of the clusters are different from expected in electrostatic models. The 3D transition has not yet happened: the calculated ground state structures of (AgBr)(n) less than or equal to 6 clusters are quasi two-dimensional. Our work rationalizes the part of covalence in the Ag-Br interaction and the role of d electrons of silver. The known abundance of trimers in the vapor of silver bromide, but, also of other silver and cuprous halides is for the first time explained as an indirect consequence of the covalent interaction between metal ions.