[Ifeffit] Vanadium pre-edge peak fitting

Alexey Boubnov alexeyboubnov at gmail.com
Tue Dec 5 22:25:24 CST 2017

Hi Will,

I worked with the Fe K-pre-edge, following the method of Wilke et al. (e.g.
ref 20 in the Chaurand paper). Letting the peaks fit freely (but with
shared FWHM and Gaussian/Lorentzian ratio) gave the best results. A few
reasons to rely on the fitting program to give you the numbers:

 - The best number of peaks to fit can be affected by the resolution of
your measurements. Crystal field theory might predict a specific number of
transitions, but you might have non-local transitions, impurities, etc.
that add extra peaks. Also, predicted transitions can be too close together
to be fitted with individual peaks.
 - The Gaussian broadening and contribution (coming from the beamline
resolution) is not always well-known.
 - The Lorentzian broadening and contribution (coming from core-hole
lifetime-broadening, traditionally taken from theoretical values of Krause
and Oliver in 1979) is also not easy to apply together with all unknowns
mentioned above.

As Chris mentioned, it is worth to find a good function to model the main
edge. You can safely do that before fitting the pre-edge (ignoring the
pre-edge peak). An arctangent + low-slope straight line + possibly a peak
function should do the job.

All the best.
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