ON THE NATURE OF NONSTRUCTURAL LOW-R PEAK IN FOURIER TRANSFORMS OF SOME EXAFS-SPECTRA

K-absorption spectra of kripton and zirconium are calculated considering additional monopole excitations of 3d-shell. It is shown that the disturbance of smoothness of the atomic photoionization cross section due to multi-electron excitations including 3d-shells lead to the appearance of low frequency EXAFS-oscillations that do not correspond to the structure of atomic encirclement of the absorber. Such an effect can make data analyses difficult for the spectra with weak structural signal

THEORETICAL INVESTIGATION OF THE INFLUENCE OF ELECTRON SHELLS' REARRANGEMENT ON K-EMISSION SPECTRA INTENSITIES IN 3d -METALS

We show that taking monopole rearrangement of electrons' shells into consideration when calculating K-spectra intensities lead to 15 - 30 % increase of calculated intensity ratio IKβ5/IKβ1 that is being used as a standard value when determining p -electron densities of valency states on 3d metals i n compounds

Double photoexcitation processes at the near K-edge region of Ne, Na and Ar

K-absorption structures were calculated for Ne, Na and Ar within the region of photo-double excitation/ionization. Ionization cross section were calculated using the theory of non-orthogonal orbitals and the energies were obtained via configuration interaction method. Calculated spectra are in good agreement with the experiment. It is shown that to describe photoionization probabilities it suffices to take into account the monopole rearrangement of electron shells. In order to interpret the fine structure of the experimental spectra one must consider angular correlations in the movement of both core and excited electrons as well as the fact that the single and multiple ionization channels open at specific energies.Nous avons calculé la structure fine du spectre de photoabsorption en couche K de Ne, Na et Ar dans le domaine de la photoexcitation simple et photoionisation double. Pour calculer les sections efficaces d'ionisation, nous utilisons la théorie des orbitales non orthogonales, et pour calculer les énergies nous utilisons la méthode de l'interaction de configuration. Nous avons obtenu un bon accord entre spectres calculés et mesurés. On a montré que pour une bonne description de la probabilité de l'effet photoélectrique en couche interne, il suffit de tenir compte du réarrangement monopolaire des couches électroniques. L'interprétation de la structure fine des spectres étudiés impose de prendre en considération une corrélation angulaire des électrons du cœur et des électrons excités pendant le mouvement. De même, il faut tenir compte du fait que les voies d'ionisation simples et doubles possèdent des seuils différents