Near edge x-ray spectroscopy theory. Annual progress report, 1993--1994 Page: 4 of 13
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I. PROJECT DESCRIPTION: Near-edge X-ray Spectroscopy Theory
A. Overview
One of our long term goals is to attain a quantitative theory of deep core x-ray
spectroscopies, including for example, x-ray absorption fine structure (XAFS),1
photoelectron diffraction2 (PD), and a new spectroscopy we have helped develop,
diffraction anomalous fine structure (DAFS).3 Since they share in common the
same excited state electronic structure, all of these x-ray spectroscopies have sim-
ilar theoretical underpinings, and are described in terms of a many-body curved
wave multiple scattering (MS) problem. These spectroscopies are valuable probes
of local atomic structure, especially in non-crystalline materials, where conven-
tional diffraction techniques are inapplicable. However their interpretation gen-
erally requires very accurate theoretical models or experimental standards. Now
with the development of our fast x-ray spectroscopy codes FEFF,4-6 we have
taken a giant step toward that goal. This project is important to the DOE mis-
sion because of scientific interest in the theory itself; the increasing use advanced
synchrotron radiation facilities by physicists chemists and other scientists; and
the significant technology transfer provided by our work. Our project had an
overall rating of outstanding (9.0) by the DOE Assessment Office in 1993, which
is within the highest priority category for continued funding.
There has been considerable progress in recent years in the development of
quantitative theories of x-ray spectroscopies such as EXAFS,7'0 XANES,11-16
(x-ray absorption near edge structure) and many other x-ray spectroscopies.
However, these theories all have limitations that usually restrict their use to one
or the other regimes. There has also been progress in understanding the complex
many-body processes that affect these spectroscopies,7 but such effects are han-
dled rather crudely in most codes. One of the aims of our project is to overcome
such limitations, and unify EXAFS and XANES (we have introduced the term
XAFS to cover both regimes"8). Our approach has been to develop, in parallel2
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Near edge x-ray spectroscopy theory. Annual progress report, 1993--1994, report, March 1, 1994; Seattle, Washington. (https://digital.library.unt.edu/ark:/67531/metadc1318961/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.