[Ifeffit] Ifeffit Digest, Vol 67, Issue 12

[Adam Webb]

Hi,

As I said in my post, I was assuming a linear relationship. I should add
that I completely agree with everything that Matt has said. I also find
it a little odd that you don't already get the data in energy from the
monochromator or from the software used to run it. You need that
time-energy relationship and the details of how the scan is made and can
not simply make an assumption. It is possible to do many things to your
data as I demonstrated but it is not necessarily the correct thing to do.

cheers,
Adam

Matt Newville wrote:
> Syed, Adam,
> 
> I think the suggestion from Adam and one of the suggestions from
> Anatoly assume the energy linear in time.  Is that the really case?
> For quick-scanning modes, many beamlines run the mono at a constant
> angular velocity, so that time maps linearly to angle, which then
> needs to be converted (non-linearly) to energy.  Then again, some
> quick-scanning beamlines use a special cam drive, in which neither
> angle nor energy would be linear in time.
> 
> Again, you need know these details in order to correctly assign
> energies to the data.  None of it is particularly difficult, so
> there's no point in guessing, and stretching or massaging the energy
> scale until two energy points correct does not mean the rest are
> correct.    You need to find out from the beamline how the data mapped
> onto energy and fix that.   While you can probably use Ifeffit macros
> within Athena to do this correction, this is really a job for the
> beamline, not for Athena.  Having an option in Athena that allowed the
> user to say "I don't know why my energy scale is bad, but can you
> please stretch the energies so that these two energies are what I'd
> like them to be" is a horrible idea.
> 
> --Matt
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