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Projects / Programmes source: ARIS

Study of collective photoexcitations for XAFS structural analysis

Research activity

Code Science Field Subfield
1.02.05  Natural sciences and mathematics  Physics  Medium- and high-energy physics 

Code Science Field
P230  Natural sciences and mathematics  Atomic and molecular physics 
Keywords
X-ray absorption, multielectron photoexcitations, structure analysis, EXAFS
Evaluation (rules)
source: COBISS
Researchers (2)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  06892  PhD Jana Padežnik Gomilšek  Physics  Head  2002 - 2004  196 
2.  10034  PhD Matjaž Štuhec  Physics  Researcher  2002 - 2004  91 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,044 
2.  0795  University ob Maribor, Faculty of mechanical engineering  Maribor  5089638010  23,989 
Abstract
Technologically important new materials often exhibit low structural order, and x-ray absorption methods (EXAFS, XANES) provide the only means of structural analysis. The acuracy of the method depends crucially on the knowledge of intra-atomic effects, i.e. on measured or numerically extracted atomic absorption spectra comprising sharp features of multielectron excitations.The coupled motion of electrons in an atomic system leads to correlation effects which are poorly described by theoretical models. The bulk of data has been obtained in direct experimental studies, mostly by x-ray absorption spectrometry of structureless or disordered samples. The optimum case is represented by monatomic noble gases and, as a recent achievement, by monatomic vapors of some volatile metals. Several suboptimal sample preparations, notably liquids, gels and glasses, have also yielded good results. After a decade of intensive studies of the subject in Slovenia, the present project concentrates on preparation and absorption spectrometry of atomic samples which can provide purest atomic absorption spectra, i.e. those with the smallest ambiguity introduced by the removal of the residual structural signal. The samples include monatomic vapors of elements with closed d-subshell (Zn, Cd and Hg), and simple molecular gases of p-series elements (H2S, HCl, SnH4, SbH3, TeH2, SeO2). Samples with a weak structural signal applicable to majority of elements are aqueous solutions of ionic species and their complex derivatives.The expertise of the project team includes also the computation with Hartree-Fock in Dirac-Fock self-consistent models whereby the features of collective effects in absorption spectra can be identified as excited states, so that the transition probabilities of individual reaction channels are determined from the experiment. The ordered data can be used to test advanced theoretical models of electron correlation, and also for semiempirical synthesis of XAFS background profiles for elements which are not amenable to direct measurement.
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