Modélisation classique de champs de forces d’interactions additives dans les agrégats de type X⁺ Ar_n, (X = Li et K); mécanisme de croissance

Abstract

The structure and stability of the Li+Arn and K+Arn clusters are studied using pair additive potentials adapted to reproduce the ab initio calculations that we estimate as the most accurate for the Li+Ar, K+Ar, and Ar–Ar dimers. The exploration of the potential energy surfaces of the Li+Arn and K+Arn systems was carried out with Wales’ method, which includes Monte-Carlo and deformation methods. From a structural point of view, one identifies a construction mechanism in very good agreement with the interpretation of the mass spectrum done by Velegrakis, including a difference for the n = 10 case. The study of the relative stability of these structures yields magic numbers for n = 8, 10, 14, 16, 18, 20, 22, 30, 32, and 34, which are in good agreement with the experiment. [Journal translation]

One-Electron Pseudo-Potential Determination of Stable Isomers of the Li*Ar n Excited Clusters: Absorption Spectra

“…This is a significant result since it allows us to approach the structural calculations for the larger clusters in ground or excited states, which would become rapidly out of benchmark calculation reach when the cluster size increases beyond the examples shown in the present work. In our previous work [10], one can see that the situation is different for the ionic Li ? Ar n clusters, where the lithium ion, which is much smaller, is located inside the argon cluster because the minimum energy of the adiabatic potential between the Li ?…”

“…Ar n clusters, where the lithium ion, which is much smaller, is located inside the argon cluster because the minimum energy of the adiabatic potential between the Li ? and the argon atom is (2,306 cm -1 ) deeper than the interaction energy between the two argons (99 cm -1 ) [10]. Table 2 presents the calculated properties of LiAr n .…”

“…Obviously the electronic screening decreases for higher excitation levels corresponding to a more diffuse excited electron orbital. For 4s states the mean orbital radius 19.07 Bohrs, is much greater than the mean distance Li*Ar in the cluster [10]. This diffuse nature reduces the structural dependence of the electronic contribution, essentially making the core interaction impose the geometry.…”

“…These are to be compared with the typical diatomic pair equilibrium distances, which roughly determine the sizes of the clusters, namely, R LiAr * 8.75 Bohrs, R ArAr * 7.23Bohrs in the neutral clusters, or R LiAr? * 4.47 Bohrs in the case of the ionised clusters [10]. The reason why the 2s, 3s, 4s… geometries are different can be analysed by considering the fact that the Ar atom can approach the Li core through the region where the Li valence electron density is small.…”

“…Because of the essentially-nonbonding character of the individual rare gas atoms, these systems may serve as prototypes for a number of studies dealing with structural and optical properties of solvated atoms or molecules [4][5][6][7][8][9][10]. Furthermore, single-valence electron atoms provide an ideal case for theoretical calculations of the lowest excited levels of alkali atoms in rare gas clusters or matrix [11][12][13][14][15][16][17].…”