Clusters alkali atoms, shell closing

See text. The first two columns give the numbers of metal atoms at which electronic shell closings have been observed in experiment for Cs-covered C o and for pure alkali metal clusters, respectively. The columns on the right list the number of electrons required for shell closings in an infinitely deep potential well with and without a central barrier. The numbers in the different columns are mainly arranged in a manner to show correlations. 

B. Clusters of alkali atoms give shell closings... 

Experiments on noble metal clusters (Cun, AgN, Aun) indicate the existence of shell-effects, similar to those observed in alkali clusters. These are reflected in the mass spectrum [10] and in the variations of the ionization potential with N. The shell-closing numbers are the same as for alkali metals, that is N = 2,S,20,40, etc. Cu, Ag and Au atoms have an electronic configuration of the type nd °(n + l)s so the DFT jellium model explains the magic numbers if we assume that the s electrons (one per atom) move within the self-consistent, spherically symmetric, effective jellium potential. 

The second, and more important kind is the giant dipole resonance intrinsic to the delocalised closed shell of a metallic cluster. Such resonances have received a great deal of attention [684]. They occur at energies typically around 2-3 eV for alkali atoms, and have all the features characteristic of collective resonances. In particular, they exhaust the oscillator strength sum rule, and dominate the spectrum locally. 

There is now extensive evidence that all closed shell molecules, including those to be discussed here, reside in the droplet s interior and hence are classified as heliophilic. Only alkali and alkaline earth atoms and their small clusters appear to be heliophobic and remain attached at the surface of the droplets. Thus, as additional heliophilic molecules are added they will encounter and recombine with those already present in the droplet interior. This was first observed spectroscopically for SFs inside droplets consisting of 4 10 He atoms. Fig. 7.4 shows the depletion signal measured with the laser tuned to the different infra-red bands of each of the small oligomers.The resulting distribution can be invariably fitted by a Poisson distribution... 

Besides alkali metal clusters, silver clusters are in the focus of research over a long period. With its closed d shell and a single 5v electron the silver atom resembles the alkali configuration and shows a similar behaviour when it comes to cluster physics. Moreover, silver clusters are promising... 

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