[Ifeffit] fitting of S XANES with arctans and gaussians

[Robert Gordon]

Hi Matthew,

WinXAS, (Commercial program by Thorsten Ressler) does possess the 
capabilities you are seeking
but it costs E$200 for an academic/gov't license.

-R.

On 7/19/2016 5:21 AM, Bruce Ravel wrote:
> 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
>
>
>