Spektroskopische Untersuchungen an Van-der-Waals-Komplexen von Aluminium- und Galliumatomen mit Edelgasen

Abstract

Aluminum and gallium atoms have been trapped in Ne, Ar, Kr and Xe matrices and studied by optical and ESR spectroscopy at 4.2°K and slightly higher temperatures. The results indicate that both metal atoms occupy axially distorted substitutional sites in all rare gas lattices. This elongated tetradecahedral MeX₁₂ coordination is particularly stable for rare gas complexes of group III metal atoms exhibiting a single unpaired electron in their outermost p shell. From the ESR data large splittings of the aluminum and gallium p shells have been derived increasing from 1600 cm^-1 in neon to 3200 cm^-1 in xenon for both atoms. The corresponding Jahn-Teller stabilization energies E_JT (increasing from ~1.5 kcal/mole for MeNe₁₂ to ~ 3.0 kcal for MeXe₁₂) can be explained by the “ σ-π” elfect: the Van der Waals interatomic correlation energy is maximized and the repulsive exchange energy is minimized by attraction of the equatorial ligand atoms to the metal center and repulsion of the remaining ligands from the σ-anti-bonding axial positions.