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

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
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5001 Nova Gorica, Slovenia

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