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). Thi s is interpreted in the frame of ab initio DFT calculations with 19-electro n pseudopotential on silver atom. The stability, the structural and electro nic properties of (AgnBrp)((+)) (n = 6, p = n, n - 1) are examined. The str uctures of the clusters are different from expected in electrostatic models . The 3D transition has not yet happened: the calculated ground state struc tures of (AgBr)(n) less than or equal to 6 clusters are quasi two-dimension al. Our work rationalizes the part of covalence in the Ag-Br interaction an d 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 f or the first time explained as an indirect consequence of the covalent inte raction between metal ions.