Use of the Z+1-core analogy model: examples from the core-excitation spectra of CO 2 and N 2O

Abstract

The interpretation of inner-electron excitation spectra in terms of the Z+1-core analogy is also shown to be valid in the cases of CO 2 and N 2O, provided one takes account of the geometrical dependence of the term values of these systems and those of the Z+1-analog NO 2, as well as of distinctions in the exchange interaction of the valence and core NO's in the two types of systems. The lowest Rydberg excitation of the unpaired electron in NO 2 is found to involve a typical 3s orbital in the vertical spectrum (bent geometry), but a strongly mixed 3s-σ * Rydberg-valence MO in the linear nuclear arrangement with a substantially larger term value, and this fact is seen to have important consequences in the appearance of the core-excited spectrum of CO 2. In addition it is found that correlation effects are significantly different in the NO 2 ground state than for its positive ion (and related Rydberg species), with CI calculations obtaining good agreement with experiment for the first I.P. of this system, but with SCF results overestimating this quantity by 1.25 and 1.75 eV for bent and linear geometries respectively.