Theoretical C1s and O1s core shake-up spectra of CO by highly correlated QDPTCI approach

Abstract

Quasidegenerate perturbation theory within the configuration interaction approach (QDPTCI) is applied to the calculation of the C1s and O1s core shake-up spectra of the CO molecule. A detailed analysis of the excitation level needed to obtain convergent QDPTCI results in the basis set used is performed for the entire manifold of the ionic states, in both the C1s and O1s regions. The need to include at least the 5h-4p excitations in the Q perturbing space in order to approach the experimental results is pointed out. The results relative to the most extended scheme used (6h-5p Q perturbing space) are compared with the experimental data. Very accurate reproductions of both the shake-up energies and spectral strengths are obtained for the C1s region. With respect to the O1s region, small discrepancies with the experimental intensities are still apparent while the excellent accord obtained between calculated and experimental energies allows one to propose the first reliable attribution of the O1s shake-up spectrum.