Effect of interference inside surroundings on XANES. O K-shell photoabsorption in N2O

Abstract

In this work an interference picture occurring as a result of inner-shell ionization of an atom in a substance is examined. We focus our attention on the interference of photoelectron scattered waves inside the surroundings of an excited atom. Such interference leads to the interdependence of amplitudes of the photoelectron waves reflected (or back scattered) by different coordination spheres and thus the surroundings act as an indivisible system. The influence of this interference is analysed here using as an example, the O K-shell XANES in the N2O molecule (the case of XANES of a terminal atom in a linear triatomic molecule). To reveal the role of the interferencial effects inside the diatomic fragment ⟨N1-N2⟩ we obtain an approximate analytical expression for XANES description. Such a description becomes possible due to (i) the localized orbitals approach, (ii) the variable phase approach and (iii) the concept of electron-optical properties of surroundings. The performed calculations show that for the correct O K-shell XANES interpretation the interference photoelectron waves inside the fragment must necessarily be taken into account. It is as well stated that the interference effects inside the surroundings explain: (1) the disturbance of the linear correlation between σ-resonance position and bond length, (2) the transformation of the EXAFS-like band to the resonance-like line in the spectrum and (3) the appearance of the extra maximum in the σ-channel of the photoabsorption cross section.