Scattering of Ions V. Elastic Scattering of the Symmetric Rare Gas Ion — Rare Gas Atom Systems

Abstract

Differential cross-sections for the elastic scattering of Ne⁺ on Ne, Ar⁺ on Ar, Kr⁺ on Kr, and Xe⁺ on Xe have been measured. In the lab.-energy range from 3 eV up to 30 eV a rainbow maximum was observed and attributed to the attractive ground state potentials of these systems. From the angular positions of the primary rainbows the potential depths were derived. In the case of Ne₂ ⁺ and Ar₂ ⁺ these values are compared with the results of quantum chemical calculations and of semiempirical estimates. From lowest energies up to Eʟ = 200 eV g-u-interference oscillations were observed for all systems. In the case of Ne⁺ -Ne two oscillatory structures with different frequencies were detected and attributed to interference between Π-states and Σ-states, respectively. With increasing atomic number of the rare gas atoms the g-u-structure becomes increasingly irregular. The measured angular distances were used to derive the potential energy difference between the interfering molecular states. The evaluation was carried out by varying parameters of analytical model potentials for the lower lying state and the difference potential until the quantum mechanically calculated differential cross-section agreed with the experimental one within the experimental error. In the case of Ne₂ ⁺ and Ar₂ ⁺ the results are compared with ab initio calculations and experimental results of other authors. For Kr⁺ -Kr and Xe⁺ -Xe a fit at all energies could not be obtained with a single set of parameters. This effect and the high irregularity of the experimental curves are attributed to fine structure splitting of the molecular states via the strong spin-orbit coupling in Kr and Xe