[Ifeffit] Transferabillity of So2

Mon Mar 23 03:50:09 CDT 2009

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
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Ifeffit mailing list
>Ifeffit at millenia.cars.aps.anl.gov
>http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>  
>

-- 
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.arcon at p-ng.si
http://www.p-ng.si/~arcon
http://www.p-ng.si/~arcon/xas

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://millenia.cars.aps.anl.gov/pipermail/ifeffit/attachments/20090323/62def8ed/attachment.html>