Chemical shifts of small heterogeneous Ar/Xe clusters

Abstract

Heterogeneous rare-gas clusters produced by a coexpansion of an argon/xenon mixture have been studied using synchrotron-radiation-based photoelectron spectroscopy. Both valence and Xe 4d 5/2 core-level photoelectron spectra were recorded for three different concentrations of the primary argon/xenon mixture and, for those mixtures, spectra were recorded at several different stagnation conditions. The studied size regime of the mixed clusters ranges from large, similar to those studied in an earlier paper [Phys. Rev. A 69, 031210(R) (2004)], to very small-as reflected in the cluster line shapes and chemical shifts. The chemical shifts obtained from a curve fitting procedure similar to that used in our earlier paper are discussed in terms of the mixed cluster structure which can be expected from equilibrium considerations and the Lennard-Jones parameters of the constituent atoms. Molecular dynamics simulations of the vertical polarization shifts allow more specific assignments of "on-top" sites and interfacial sites.

A detailed investigation on the global minimum structures of mixed rare‐gas clusters: Geometry, energetics, and site occupancy

“…For instance, the structures Ar 14 Xe 24 and Kr 5 Xe 33 have one or more smallest‐atoms in the core of the cluster (which may be associated with abrupt variations of the strain parameter), but such atoms tend to segregate to the surface for N ≥ 23. Moreover, the experimental observation that argon atoms segregate to the surface in Ar–Kr[10, 12] and Ar–Xe[14, 16] clusters is corroborated by the global minimum structures obtained for most of the compositions (i.e., values of N ) considered in this theoretical investigation.…”

“…Also, heterogeneous rare‐gas clusters have been investigated by the electron diffraction technique, but in this case the preparation of the aggregation is more complex[7–9] and the structure of the cluster is dependent on the method of production. [10, 11] In turn, both photoelectron and optical spectroscopic experiments have been carried out to study mixed Ar–Kr[10, 12, 13] and Ar–Xe[14–16] clusters formed by coexpansion of a gas‐mixture. It has been found in these experiments that mixed Ar–Kr and Ar–Xe clusters lead to structures with argon atoms mainly occupying surface sites.…”

Structural distribution in mixed ternary noble gas and Lennard-Jones clusters

“…For instance, mass spectra of Ar, Kr, and Xe clusters, grown neutral and ionized by electron impact, up to cluster size n = 1000 were presented, and the most pronounced ''magic numbers'' in the distributions of large cluster ions occur at n = 147 (148 for Ar), 309, and 561 [1]. Clusters of heterogeneous materials show a much richer behavior than their homogeneous counterparts [5], and the geometric and electronic structure of mixed clusters enables studies of photochemistry [6].…”

Soft X-ray absorption spectroscopy of Ar2 and ArNe dimers and small Ar clusters

“…Indeed, many of the pioneering studies of this field have involved the core-hole spectroscopy of Ar-containing rare gas clusters. 11,12 Theories used to describe the shifts of core-excitation transition of atoms embedded in rare gas clusters or at surfaces 8,[13][14][15] are often based on the modelling of the interaction of the Rydberg electron with the ion core (e-Rg + core ) and that of the interaction of the Rydberg electron with the surrounding lattice (e-Rg crystal ). The first XAS studies 5,6 of Ar clusters involved scanning the synchrotron radiation in the L 2,3 region while recording electron and ion yields and varying the cluster size from few up to 750 Ar atoms.…”

“…8 Subsequent experimental work provided further detailed measurements of the XAS spectrum in the L 2,3 region both in pure Ar clusters 9,10 and in heterogeneous clusters containing mixtures such as Ar/Kr, Ar/Xe and Ar/N 2 . 11,12 Theories used to describe the shifts of core-excitation transition of atoms embedded in rare gas clusters or at surfaces 8,[13][14][15] are often based on the modelling of the interaction of the Rydberg electron with the ion core (e-Rg + core ) and that of the interaction of the Rydberg electron with the surrounding lattice (e-Rg crystal ). The potentials used to describe these interactions are based on model potentials where, for example, the e-Rg + core potential can be described by the Kleinman-Bylander pseudopotential 8,16 and the e-Rg crystal is described by a model potential based on the sum of short and long range forces with the parameters adjusted to describe the low energy electron-Rg scattering (see ref.…”