Hi Skya, On Thursday 06 September 2007, Skya Fawcett wrote:
A couple questions about linear combination fitting in Athena:
1. There is the option of floating an E0 for the standards, is there any way to restrict how much it floats, ie. constrain it to +/-0.4eV shifts during fitting?
The e0s can be floated -- that's what the "fit e0" column is all about in the table on the LCF page: http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/analysis/lcf.html Alternately, you can click the "All standards use the same e0" button, which is the same thing as applying an e0 to the data but not to the standards. There currently is no way to apply the sort of constraint that you want in Athena. (The same is not true of Ifeffit. If you were to use Ifeffit directly, you could build a XANES fitting model that imposes that constraint. But Athena does not provide a way of doing so within its GUI.) My standard comment on this topic is that if you take care to align all of your data and you have the right set of standards, e0 shifts should not be necessary.
2. If I am fitting normalized u(E), and only care about the XANES region at this point, is perfecting background removal needed? (I have, of course, carefully checked the pre-edge and normalization range).
Nope. The XANES LCF fitting uses the normalized spectra. That is independent of how the background is removed. Sounds like you are doing the right thing. HTH, B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/