[Ifeffit] two measurements of the same compound in different beam-lines

[Scott Calvin]

Hi Maria,

You have several choices. First, note that the merge function in  
Athena allows you to select options of weight by chi-noise, or weight  
by importance. If you weight by chi-noise, noisier data will be  
counted less. If you have some other way of estimating the quality of  
the data sets, you can enter different numbers in the "importance"  
field and then weight by importance.

If working on two different beamlines, you might consider merging  
chi(k) data, rather than norm(E), as the backgrounds may be different.  
And mu(E) probably makes no sense at all.

Another option is to obtain separate chi(k)'s, but then fit both  
spectra simultaneously in Artemis. The Artemis/Ifeffit default  
behavior in that case will be to use high-R noise for weighting, but  
you can override that by assigning an epsilon to each data set if you  
choose. This method has several advantages: it lets you see if one  
data set is fitting differently from the other; it lets you choose  
different k-ranges if noise begins dominating one data set at a lower  
value of k; it lets you use different values of S02 if there are  
pinhole, harmonic, or self-absorption effects; and it lets you use  
different values of delE0 if the data sets are hard to align properly.

--Scott Calvin
Sarah Lawrence College


On Aug 12, 2010, at 8:44 PM, María Elena Montero Cabrera wrote:

> Hi all!
> I have performed two independent XAFS measurements of Cr K-edge of  
> the same Fe-Cr sample at two different beam-lines at SSRL. I have  
> obtained the Fe-K edge data only once. The quality of data are  
> different in each measurement. However, I cannot average spectra  
> from different Cr-K measurements, and I don't know if I could take  
> somehow advantage from having almost twice the information for the  
> Cr- K adge, or I have to use only the better quality data and  
> discard the other. What do you advice? If I can use both  
> measurements, how can I do the fitting in Artemis?
> Thank you very much and all take care
>
> -- 
> María Elena
>
> Dra. María Elena Montero Cabrera
> Departamento de Medio Ambiente y Energía
> Centro de Investigación en Materiales Avanzados (CIMAV)
> Miguel de Cervantes 120, Compl. Ind. Chihuahua
> Chihuahua CP 31109, Chih. México
> Tel (614) 4391123
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