[Ifeffit] The dependence of So2 on neighboring atoms

Matt Newville newville at cars.uchicago.edu
Thu Apr 30 23:17:41 CDT 2009

Hi JeongEunSuk,

> It is known that So2 is the relaxing factor of passive electron.
> So I think that So2 is affected by neighboring atoms because the potential
> is made by those
> Especially, If neighboring atoms are heavy atoms, the contribution will
> increase. Is it right?
> If it is right, what is the dependence of So2 on neighbor atoms?

Usually S02 is separated from other loss terms as the "passive
electron" factor, to account for the relaxation of the other Z-1
electrons to the sudden presence of that 1 core hole that the
absorption process created.  In this view, it is purely an effect of
the absorbing atom, and is not affected by the neighboring atoms.

In a quantum mechanical view of Fermi's Golden rule, absorption is a
transition of an atom from an initial (ground) state of an atom to a
final (excited) state of the atom.  Most of the change is the presence
of that core hole (which gives the edge jump), a lesser part of the
change comes from the created photo-electron interfering with the
neighbor atoms (which gives the EXAFS), and a smaller part yet comes
from the Z-1 electrons of the atom relaxing to the presence of the
core hole (which gives S02).

You are right that the highest energy-level electrons of atom (ie,
those least bound to the atom), will interact with neighboring atoms,
and therefore change the potential.  From the point of view of deep
core levels, the chemical bonding of the valence-level electrons is a
pretty small perturbation and is generally ignored when considering

Of course, for analysis, the S02 parameter is more or less a fudge
factor covering up some sins in the measurement and other sins in the
approximations in the calculations for the loss terms.


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