Repulsive Coulomb Barriers in Compact Stable and Metastable Multiply Charged Anions

Abstract

We demonstrate that a simple Coulomb-energy model can be used to predict the vertical electron detachment energy of an anion of charge (−n) given the detachment energy of the corresponding anion having one less charge (−n + 1). This model was applied earlier by other workers to dianions in which the two charged sites are quite distant. In this paper we show that it can also be applied to more spatially compact species as long as the two orbitals from which the electrons are removed are sufficiently noninteracting. We first demonstrate how to use this model by applying it to a series of electronically stable dianions (MgF42-, BeF42-, TeF82-, SeF82-, and TeCl82-) for which the (−2) to (−1) and (−1) to (neutral) electron detachment energies have been evaluated using conventional ab initio methods. These test calculations allow us to assess the predictive accuracy of the Coulomb model. We then extend the model's use to predict the energies of dianions and trianions that are not electronically stable (SO42-, CO32-, PO43-, and PO42-) and for which application of conventional quantum chemistry methods will not yield reliable predictions. That is, we predict at what energies metastable resonance states of these species will occur. Finally, we use the Coulomb nature of the long-range part of the electron−anion potential to estimate the lifetimes of these resonance states with respect to electron loss.