[Ifeffit] Energy Resolution

[Julian Ehwald]

Hi Carlo

Thank you for your answer. I have completely different question as well: I
just started using Artemis, and have a question regarding the amplitude
reduction factor: I use different So^2 for different elements, correct? If I
start fitting and have paths involving the same kind of atom but once at
distance 2A, and once maybe 3A, is this then the same So^2 or am I supposed
to model the behaviour of So^2 somehow?
Similar for \Delta R: If I don’t have a nice simple cubic structure and
can’t use isotropic expansion similar like alpha*R_eff, what would be a
smart(or physically correct) way to connect \Delta R (as well as sigma^2)
for the same element for different distances? The material I am looking at
is Li2O2 and Li2IrO3, which don’t have a very simple structure.

I am aware that maybe I am asking a bit much, but if you could help me in
any way I would be very delighted. 

Best, Julian

-----Ursprüngliche Nachricht-----
Von: Ifeffit [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] Im Auftrag
von Carlo Segre
Gesendet: Sonntag, 6. Mai 2018 01:07
An: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
Betreff: Re: [Ifeffit] Energy Resolution


Hi Julian:

With an edge energy of 543 eV, your monochromator resolution should be at
least 0.1 eV.  If you are interested in XANES, you need to take data at this
resolution or maybe even better.  ONce past the edge, there is no need to
keep that step size.  If your beamline permits an EXAFS-type step scan with
steps in k-space, you want to use a dk of 0.05 which is what IFEFFIT
interpolates to.  Smaller step sizes are not really useful.

Carlo

On Sat, 5 May 2018, Julian Ehwald wrote:

> Dear all,
>
>
>
> This might be a very general question, but: I was wondering what 
> energy resolution you typically use at beamlines to obtain your raw data
for exafs.
> Since we have limited Beamtime only and other experiments that we want 
> to carry out, I was wondering what kind of resolution is common. Or
> differently: Is it predictable what happens if I for example change 
> from steps of 0.2eV to 0.4eV? We want to obtain spectra up to 500eV 
> above Oxygen K, if that is of relevance.
>
> Best, Julian
>
>

--
Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair,
Department of Chemistry Director, Center for Synchrotron Radiation Research
and Instrumentation Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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