Advanced Computation Method for Double Core Hole Spectra: Insight into the Nature of Intense Shake-up Satellites

Abstract

Double core hole spectroscopy is an ideal framework for investigating photoionization shake-up satellites. Their important intensity in a single site double core hole (ssDCH) spectrum allows the exploration of the subtle mix of relaxation and correlation effects associated with the inherent multielectronic character of the shake-up process. We present a high accuracy computation method for single photon double core shell photoelectron spectra that combines a selected configuration interaction procedure with the use of non orthogonal molecular orbitals to obtain unbiased binding energy and intensity. This strategy leads to oxygen ssDCH spectrum of the CO molecule that is in excellent agreement with the experimental result. Through a combined wave function and density analysis, we highlight that the most intense shake-up satellites are characterized by an electronic reorganization that opposes the core hole induced relaxation.

Communication: Multi-reference Approach to the Computation of Double-Core-Hole Spectra

“…We tested our approach by computing the ssDCH spectra of CO, H 2 O, N 2 and of the C 2 H 2n (n =1-3) series, and comparing our results with available experimental data 15,17,23 .…”

Communication: Multi-reference Approach to the Computation of Double-Core-Hole Spectra

“…Its characteristics upraise ssDCH spectroscopy as one of the most promising techniques to chemical analysis. However, in contrast to SCH spectroscopy [19][20][21][22] , it has been widely demonstrated that some of the most important features of a typical DCH spectrum arise from strong shake-up satellite states 14,17,23 , which stem from excitation of one or more outer electrons in combination with the photoionization of two core electrons located on the same atom. Shake-up satellite states have intrinsic multielectronic character and are strongly affected by relaxation and correlation effects [24][25][26] .…”

“…It was only recently that an accurate method to compute ssDCH binding energies as well as spectral strengths was proposed by Ferté et al and applied to the CO molecule 23 .…”

“…φ A p |φ B q = δ pq 59 . When this is not the case, like in the work of Ferté et al 23 , the more complicated Löwdin's rules have to be used to compute φ A p |φ B q and then S µν 67 .…”

“…The sudden approximation should be a good approximation for high kinetic energies of the photoelectrons, as it generally happens to be the case far above the double core ionization potential. We tested our approach by computing the ssDCH spectra of CO, H 2 O, N 2 and of the C 2 H 2n (n =1-3) series, and comparing our results with available experimental data 15,17,23 .…”