First observation of a tetra-anionic metal cluster, Aln4−

Abstract

The production of aluminum cluster tetra-anions, and thus the first observation of a tetra-anionic metal cluster in the gas-phase, is reported. The aluminum cluster polyanions were generated by use of the "electron-bath technique." The smallest tetra-anion observed was Al(215) (4-), containing 14% fewer atoms than expected from classical estimates of the tetra-anion appearance size.

Abundances of Tetra-, Penta-, and Hexa-Anionic Gold Clusters

“…This discrepancy was resolved by introducing a correction δ > 0 for the electronic spill-out 42 to the cluster radius, motivated by the increased electron-electron repulsion in a highly negatively charged cluster. [36][37][38] This leads directly to the second step of the present approach. The stability of a poly-anion increases with the size of the cluster, i.e.…”

“…calculations are performed for T = 0 K. Corresponding approaches were used for calculations on small, solid particles, 33 and have been applied to describe the observed poly-anion abundances of metal clusters close to room temperature. 31,[34][35][36][37] While a rather smooth increase of abundance is observed for meta-stable poly-anions as a function of cluster size, calculated lifetimes predict a much sharper slope. 38 In other words, the clusters are less stable with respect to electron emission than predicted from the 0-K field-emission model.…”

Electron attachment to anionic clusters in ion traps

“…Later, di-, tri-, tetra-, and penta-anions of aluminum clusters were observed [14,15,30,31]. With the recent upgrade of the ClusterTrap setup to a 12-T Penning trap, higher charge states for gold clusters have been reported, reaching from tetra-up to hexa-anions [17,18].…”

“…Besides the cluster-size criterion [3,13,18,28], the maximum charge state and the relative yields of the polyanionic species are to some extent controlled by the trapping potential depth, which limits the energy of trapped electrons [14,[31][32][33][34], and by the reaction time [31,34] as shown for the case of gold clusters (Fig. 5a).…”

“…For example, doubly charged anions of carbon and metal clusters were produced either in ion sources by sputtering [4], laser ablation [5][6][7], and electrospray ionization [8], or by electron-transfer reactions [9,10], and in crossed-beam experiments [11]. While also tri-anionic lead clusters were observed by laser ablation [7], even higher charge states have been produced of gold and of aluminum clusters by their simultaneous storage with electrons inside a Penning trap [12][13][14][15][16][17][18]. Recently, production of di-and trianionic gold clusters in a linear radio-frequency quadrupole (RFQ) trap has been demonstrated by exposing stored monoanions to an electron beam [16,17].…”