I am aware of two examples in the literature where EXAFS have been fit without and with consideration of multielectron excitation. Both Found a 0.01 - 0.02 A contraction in the first shell scattering pathlength when the multielectron effects were removed. The relevant papers are: P. D'Angelo, H.-F. Nolting, and N. V. Pavel, Phys. Rev. A, 53 (1996) 798 J.A. Solera, J. Garcia, and M. G. Proietti, Phys. Rev. B, 51 (1995) 2678 In the second paper they show that the effect of multielectron excitations for the lanthanide-aquo ions is unimportant in the fitting of the EXAFS for lanthanides heavier than samarium, and that the multielectron excitations are not even visible by the time one reaches dysprosium. ------------------------------ Mark P. Jensen Chemistry Division Argonne National Laboratory 9700 South Cass Avenue Argonne, Illinois 60439-4831 USA 630-252-3670 630-252-7501 FAX mjensen@anl.gov
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Barton, David G. Sent: Wednesday, July 13, 2005 9:30 AM To: 'XAFS Analysis using Ifeffit' Subject: RE: [Ifeffit] multielectron transition
Iztok,
This is good stuff. Mulitelectron features definitely throw at least a small wrench in a typical background substraction routines that only substract smooth, broad features using splines.
My naïve questions are: 1) What chemical elements show a sizable contribution from a multielectron feature that could skew spline based EXAFS data analysis routines? 2) Are there any examples in the literature where a spline-based EXAFS analysis (i.e. bond lengths, coordination numbers with statistics) is performed on a more complex system than with and without the removal of these multielectron features as a comparison.
Dave
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Iztok.Arcon@p-ng.si Sent: Wednesday, July 13, 2005 10:21 AM To: bravel@anl.gov; XAFS Analysis? using Ifeffit? Cc: QY ZML; XAFSA Analysis usingI Ifeffit Subject: Re: [Ifeffit] multielectron transition Importance: Low
Dear Bruce
An example of treating atomic absorption background including large multielectron features in L edge spectra of Ce is given in the attached paper. Full atomic absorption background for nearby elements Cs and Xe can be seen in the second attached paper. Some other useful references on this topic are given below:
J. A. Solera, J. Garcia, M. G. Proietti, Phys. Rev. B 1995, 51, 2678–2686.
A. Kodre, I. Arčon, M. Hribar, M. Štuhec, F. Villain, W. Drube, L. Troeger, Physica B 1995,208&209, 379–380.
J. Padežnik Gomilšek, I. Kozjek Škofic, N. Bukovec, A. Kodre, Thin Solid Films 2004, 446, 117–123.
E. Fonda, D. Andreatta, P. E. Colavita, G. Vlaic, J. Synchrotron Rad. 1999, 6, 34–42.
also some our references for atomic absorption spectra of K edge exafs:
A. Kodre, I. Arčon, J. Padežnik Gomilšek, R. Frahm Multielectron excitations in x-ray absorption spectra of Rb and Kr J. Phys. B: At. Mol. Opt. Phys. 35 (2002) 3497-3513
A. Kodre, I. Arčon, J. Padežnik Gomilšek, A. Mihelič Atomic absorption background in EXAFS spectra of Rb in inter-alkaline alloys Physica Scripta. Vol, T115, (2005) 218-220
A. Kodre, R. Prešeren, I. Arčon, J. Padeznik Gomilšek, M.. Borowski, A study of transferability of atomic background on EXAFS spectra of simple gaseous compounds of As, J. Synch. Radiation 8 (2001) 282-284
R. Prešeren, A. Kodre, I. Arčon, M. Borowski, Atomic background and EXAFS of gaseous hydrides of Ge, As, Se, and Br, J. Synch. Radiation 8 (2001) 279-281
There are many other papers of different authors on the multielectron photoexcitations (see references in above papers). Additional information on multielectron photoexcitations in exafs spectra of L and K edges of different elements and some subtraction procedures can be found also on the dedicated web site of our group:
http://www.p-ng.si/~arcon/xas/mpe/mpe5.htm
best regards and congratulations for well supported program packages for exafs analysis.
Iztok Arcon
On Tuesday 12 July 2005 11:18, QY ZML wrote:
I am analyzing EXAFS of some rare earth systems. It is known that there are ?multielectron transitions in these systems. So, I want to know how to subtract multielectron process contribution generally and if ATHENA has a feature to do this. ?Thank you very much.
Athena does not currently have a feature for doing this. Drat!
I would be willing to implement something empirical for doing this. I would like to see a discussion here on the mailing list of the merits of different approaches. Since I have never given this very much thought, I am not with any strong opinions for how it should (or should not) be done. But I can certainly consider implementing it.
B
-- Bruce Ravel ----------------------------------- bravel@anl.gov -or-
ravel@phys.washington...edu
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My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/
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