Negative ions and shape resonances

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Abstract
A simple model potential having one adjustable radius parameter r0 is employed to obtain electron affinities and the positions and widths of shape resonances by performing an extrapolation along an isoelectronic sequence of positive ions and the associated neutral atom. The values of the parameter r0 are determined by requiring the potential to yield the experimentally observed energies of a given state of the members of the isoelectronic sequence. A quadratic extrapolation of r0-1 then provides a model potential representing the field of the atomic core on the additional electron in the negative-ion system, stable or unstable, belonging to the isoelectronic sequence. This potential is then used to determine the energy of binding of the extra electron in the negative ion, if it exists, thus giving the electron affinity of the neutral atom concerned with an accuracy to within about 0.1 eV in most cases. Metastable states of certain negative ions are considered in the same manner. The model potential is also used to investigate the elastic scattering of electrons by neutral atoms. When the potential field produced by the atomic core is insufficiently strong to bind the additional electron, p-wave shape resonances are found and the positions and widths of these have been determined. Atoms in the periodic table from hydrogen through to chlorine have been investigated.

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