[Ifeffit] fitting of S XANES with arctans and gaussians

Bruce Ravel bravel at bnl.gov
Tue Jul 19 07:21:12 CDT 2016


On 07/18/2016 11:10 PM, Matthew Marcus wrote:
> I'm trying to fit 37 micro-XANES spectra taken at the S K-edge, using
> the method discussed in the paper by Manceau and Nagy "Quantitative
> analysis of sulfur functional groups
> in natural organic matter by XANES spectroscopy", Geochimica et
> Cosmochimica Acta 99 (2012) 206–223.  In this paper, they fit spectra to
> two arctangents and 6 gaussians,
> with widths of the arctans slaved together and widths of gaussians 1-3
> and 4-6 slaved (or all 6 to one value).  I'm looking for recommendations
> as to how to do the fit.
> They give prescriptions for how to set the initial estimates to give
> robust values.  Manceau has told me that 'Athena works quite well', but
> I don't see any obvious way there
> to do the parameter constraints called for, or to keep peak heights from
> going negative.  Athena also has a habit of assuming you want it to do
> the normalization
> for you; I've already done that and need no further 'help'.  Any ideas?

Matthew,

As for the pre-normalized data, you are supposed to be able to tell 
Athena at the time of import that the data are normalized mu(E).

http://bruceravel.github.io/demeter/documents/Athena/import/columns.html#data-types-and-energy-units

If that doesn't work, let me know.

As for constraints in the peak fitting, that is certainly not 
implemented in Athena.  I am not quite sure why Alain thinks otherwise.

HTH,
B



-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 743, Room 114
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/


More information about the Ifeffit mailing list