[Ifeffit] Spectra for ions?

Bruce Ravel ravel at phys.washington.edu
Thu Jan 22 16:14:04 CST 2004

On Thursday 22 January 2004 04:56 pm, k-kupiecki at northwestern.edu wrote:
> When we pulled up his data in Athena it looked very weird since it looked
> like Athena was expecting it to be over a range of energies applicable
> for EXAFS.

I presume that what you mean by this is that the grid spacings in the
x-axis array are not something consistent with exafs -- i.e. they are
not of the order of 1.  Possibly, your data is in the form of
wavenumbers, i.e. backwards from what Athena expects as well as with
spacing != O(1).

You could try using a little script or a spreadsheet to change the
x-axis array so that each step is of order 1.  It need not start at a
value in the 1000s.  Athena reads, for example, dispersive data taken
on a position sensitive detector just fine.  In that case, the data
starts at 1 and is on a uniform, integer grid.  After Athena is done,
you could then use a script or a spreadsheet to convert it back to the
original x-axis grid.

This actually raises an interesting point about a feature that is
missing from Athena.  Athena gives you no ability to preprocess the
x-axis grid (other than automatically detecting and converting from
keV to eV).  It would be very nice to be able to specify a math
expression for converting a data array to an energy grid.  That would
be useful, for instance, if you wanted to read an array of encoder
valuess and use that as your energy array.  That sort of generic data
preprocessing has long been on Athena's list of things to do.  IIRC,
Sam's SixPack has a feature like this.  Perhaps that and Sam's
interface to the Autobk algorithm would do the trick for you.  Worth
looking into, in any case.


 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
 Code 6134, Building 3, Room 222
 Naval Research Laboratory                          phone: (1) 202 767 5947
 Washington DC 20375, USA                             fax: (1) 202 767 1697

 NRL Synchrotron Radiation Consortium (NRL-SRC)
 Beamlines X11a, X11b, X23b
 National Synchrotron Light Source
 Brookhaven National Laboratory, Upton, NY 11973

 My homepage:    http://feff.phys.washington.edu/~ravel 
 EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

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