Evidence for trimers evaporation in silver bromide clusters

Abstract

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 ≤ 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.PACS. 36.40.Qv Stability and fragmentation of clusters -31.15.Ar Ab initio calculations

Structure and stability of coinage metal fluoride and chloride clusters (MnFn and MnCln, M = Cu, Ag, or Au; n = 1–6)

“…[54] Although the energies of the heptamers M 7 X 7 were not known, we can conclude from the present calculation that their dissociation into a trimer + a tetramer is the lowest channel for all species. The large stability of the trimers is in line with previous experiments of fragmentation of metastable silver bromide clusters[15, 16, 56] in which the evaporation of a trimer was found to be the preferred dissociation channel of Ag n Br n ‐p + ( n = 5–14, p = 1–5) clusters.…”

“…[14] The relative large stability of the trimer was also shown in experiments of fragmentation of metastable clusters in the case of silver bromides. [15, 16] The evaporation of a trimer was found to be the preferred dissociation channel of Ag n Br n ‐p + ( n = 5–14, p = 1–5) clusters. Some theoretical studies,[17, 18] within the framework of the density functional theory (DFT) have investigated the electronic and structural properties of small silver bromide clusters and showed that small stoichiometric clusters Ag n Br n ,with n ≤ 6, adopt cyclic structures and not cube‐like ones as it was supposed hitherto.…”

Ab Initio Study of Neutral and Charged Copper Bromide (CuBr) n (+) Clusters (n = 1–6)

“…In gas phase, an amazing common property of all these compounds is the unusual abundance of trimers in their vapor [4][5][6][7][8][9][10][11][12], although smaller molecules like monomers, and eventually dimers are expected for metal halides. The relative large stability of the trimer was also shown in experiments of fragmentation of metastable clusters in the case of silver bromide [13,14]. The evaporation of a trimer was found to be the preferred dissociation channel of Ag n Br n-p ?…”

The DFT study on the structures and properties of (AgBr)n (n⩽6)

“…Based on the previous studies, the aim of this work is to further and systematically study the ground state structures and electronic properties of (AgBr) n. It must be pointed out that our initial structures of (AgBr) n are not guessed, but the results of genetic algorithm (GA). Those stable structures in the literatures [20,[22][23][24] are all included in our results of GA, which indicates that our initial structures are reliable, and this method to obtain initial structures can be extended to study large-sized clusters. Those initial structures obtained by GA are further optimized by using DFT method.…”

“…The calculation indicated that the most stable geometries of (AgBr) n (n 6 9) were mainly close-packed [22]. Configuration Interaction (CI) calculation was performed to investigate the structures of neutral and single charged (AgBr) n (n 6 2) [23]. The structures and properties of (AgBr) n (n 6 6) were also explored in the framework of DFT/B3LYP with Relativistic Effect Core Pseudopotential (RECP) basis set, in which 19 valence electrons are for Ag and seven valence electrons for Br [24].…”