PREDICTION OF THE ELECTRONIC-ENERGY LEVELS OF DOUBLY CHARGED POSITIVE MOLECULAR-IONS WITH THE AID OF THE MULTIPLE-SCATTERING X-ALPHA METHOD

Approximate electronic structure calculations with the multiple scattering X-alpha method have been employed to predict the energy differences, for NH3 and N2O, between the neutral molecule ground state and energetically low-lying states of the doubly charged positive molecular ion with the neutral molecule's geometric structure. Comparison with experimental values of such vertical double ionization energies, observed with double charge transfer spectroscopy, indicates that direct application of the method gives unsatisfactory results. Instead a combination of an interaction energy calculated with the method and experimentally determined single ionization energies can predict double ionization energies to an accuracy sufficient to aid the analysis of double charge transfer spectra.