BERYLLOCENE, (C5H5)2BE - HE(I) PHOTOELECTRON-SPECTRUM AND ABINITIO MOLECULAR-ORBITAL CALCULATIONS

Ab initio molecular orbital calculations with a double-ζ basis have been carrried out on five models of beryllocene, Cp2Be, with fixed geometries. The lowest energies are obtained for the π-Cp, σ-Cp and D5d models. The He(I) photoelectron spectrum of Cp2Be was recorded and the ionization potentials of the first bands were compared with the orbital energies obtained from the molecular orbital calculations. A satisfactory fit between experiment and calculations was obtained for a slip sandwich model of Cs symmetry. A model of C5v symmetry is only compatible with the PE spectrum if the Jahn-Teller splitting of the lowest 2E1 state of the molecular ion is exceptionally large, 1.0 eV. © 1979.