Argon clusters stability

Barber et al. introduced FAB in 1981. In this technique, bombardment of a liquid target surface by a beam of fast atoms such as xenon or argon, causes the continuous desorption of ions that are characteristic of the liquid. In a typical FAB spectrum, the analyte ion is usually formed as protonated or cationized ions in positive FAB, and deprotonated ions in negative FAB mode. A few fragmented ions may also be formed. The spectrum usually contains peaks from the matrix, such as protonated matrix clusters of glycerol if it is used as the matrix solvent. FAB utilizes a liquid matrix such as glycerol. The matrix is used to enhance sensitivity and ion current stability. 

Up to the saturation of the 5-atom ring, the energy gained by each argon atom addition corresponds to the addition of a new IT-like interaction with sodium, plus the formation of an extra weak ArAr dispersion bond (two in NaArs). Beyond this size, the addition of argon atoms mainly involves the formation of ArAr bonds, and the stabilization is found to be weaker. In this respect, the stability of Na(3p)Ars is enhanced with respect to its immediate size neighbors and this cluster can be considered as an excited magic size cluster. 

Analyzing the two-color spectra of the benzene...Ar clusters for n = 1-9, the authors [35] concluded that "the hexagonal lower-shaped configuration of seven argons on one side of the benzene represents some stability limit for the (n 10) argon monolayer conformation". 

The behaviour of a large number of argon atoms represents a difficult task for theoretical description, but is still quite predictable. When the number of atoms increases, they pack together in compact clusters similar to those we would have with the densest packing of tennis balls (the maximum number of contacts). We may have to do here with complicated phenomena (similar to chemical reactions) and connected to the different stability of the clusters (e.g., magic numbers related to particularly robust closed shells ). Yet, the interaction of the argon atoms, however difficult for quantum mechanical description, comes from the quite primitive two-bo(ty, three-body etc. interactions (Chapter 13). 

Modem supersonic molecular beam techniques provide a direct way to study the stability and valence electron structure of noninteracting, isolated atomic clusters. One of the most widely studied properties is the threshold for photo-ionization and its dependence on cluster size. In Fig. 4.20 we reproduce some experimental results for argon-, krypton-, xenon- (Gantefor et al., 1989), and mercury-clusters (Rademann et al.. 

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