Dear Scott,
There are several papers dealing with effects of multielectron
photoexcitations present in atomic absorption background (AAB) of K and
L edge EXAFS spectra, which are responsible for the amplitude reduction
factor S02. A quantitative analysis of shake-up, shake-off and other
collective photoexcitation channels in the total cross section for the
photoeffect in inner shells in the EXAFS energy region (from the edge up
to 1000 eV and beyond), and the question on transferability of these
effect and consequently the transferability of AAB is addressed for
example in the papers:
*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
*J. Padežnik Gomilšek, A. Kodre, I. Arčon, A. M. Loireau-Lozac'h, S.
Bénazeth *
/Multielectron photoexcitations in x-ray absorption spectra of 4p
elements, /
Phys. Rev. A 59 (1999) 3078 - 3081
The results show that the shake-up and shake-off channels are mainly
independent on the chemical surrounding of the excited atom, while
resonant double electron excitations are very sensitive on the chemical
state (unoccupied bound final states). The effect is especially strong
in L3 edge spectra of lanthanides (for example 2p4d channels).
There are several other more recent papers of different authors which
also present results on AAB, which may be helpful in resolving the
problem of transferability of S02 and
reveal the limitations in the use of So2 amplitude reduction factor
and standard spline approximation for AAB in EXAFS analysis.
Below I mention just a few results of our group:
*J. Padežnik Gomilšek, I. Arčon, S. de Panfilis, A. Kodre,*
/X-ray absorption coefficient of iodine in the K edge region
/J. Phys. B: At. Mol. Opt. Phys. 41 (2008) 025003
<http://scitation.aip.org/vsearch/servlet/VerityServlet?KEY=ALL&possible1=Kodre%2C+A.&possible1zone=author&maxdisp=25&smode=strresults&aqs=true>*J.
Padežnik Gomilšek, I. Arčon, S. de Panfilis, A. Kodre,*
Phys. Rev. A *79*, 032514 (2009) [7 pages]
X-ray absorption in atomic iodine in the /K/-edge region
*A. Kodre, J. Padežnik Gomilšek, A. Mihelič, I. Arčon
*/X-ray absorption in atomic Cd in the K edge region
/Radiation Physics and Chemistry 75 (2006) 188-194
*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
*I. Arčon, A. Kodre, J. Padežnik Gomilšek, M. Hribar, A. Mihelič*
/Cs L-edge EXAFS atomic absorption background/
Physica Scripta. Vol, T115, (2005) 235-236
*Jana Padežnik Gomilšek, Alojz Kodre, Nataša Bukovec and Irena Kozjek
Škofic *
/Atomic effects in exafs structural analysisof mixed Ce oxide thin films/
Acta Chim. Slov. 51 (2004) 23-32
*
J. Padežnik Gomilšek, A. Kodre, I. Arčon, M. Hribar *
/K-edge x-ray-absorption spectra of Cs and Xe /
Phys. Rev. A 68 (2003) 042505
The problem is presented also on the web page:
http://www.p-ng.si/~arcon/xas/mpe/mpe.htm
best regrds
Iztok Arcon
Scott Calvin wrote:
Hi all,
One of the most universally accepted facts used in EXAFS analysis is
that the amplitude reduction factor S02 is chemically transferable.
I've been trying to find a good reference for this--either a key study
establishing it, or a review article asserting it. I know there has
been plenty of good work in recent years trying to make theoretical
calculations of S02, and that they are gradually becoming more
accurate. But these recent advances can't be the reason we treat S02
as transferable, because we've been doing it for decades.
How was this established? It seems devilishly difficult to do
experimentally with good accuracy, because S02 will correlate to some
extent with other parameters. Those correlations can be broken to
some extent by using /k/ dependence, but it seems the uncertainties
would still be somewhat high. On the other hand, were there compelling
theoretical reasons back in the 80's for believing transferability to
hold?
Currently, how good do we think the assumption of transferability
really is? Good to 5% for any compound at that edge? Good to 1% for
compounds with similar local environments at that edge? Better than
that? (I'm asking about the EXAFS region; say, more than two inverse
angstroms above the edge.)
I eagerly await your collective wisdom, knowledge, and humorous anecdotes.
--Scott Calvin
Sarah Lawrence College
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Iztok Arcon
University of Nova Gorica
Vipavska 13, POB 301
5001 Nova Gorica, Slovenia
tel: +386 5 331 5227
fax: +386 5 331 5240
e-mail: iztok.ar...@p-ng.si
http://www.p-ng.si/~arcon
http://www.p-ng.si/~arcon/xas
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