On Wednesday 22 July 2009 09:27:16 pm Richard Mayes wrote:
In cases where intense pre-edge features are observed, such as the one you attached, you should manually set the Eo and not accept the Athena defaults. I usually start with half-way up the absorption edge (you can look at the derivative and move the Eo value to the maximum in the derivative; however, make sure you don't move it back to the pre-edge).
I want to expand on one part of Richard's excellent advice. The default values in Athena are not selected by algorithms that are particularly sophisticated and they are certainly not chosen to be appropriate to a specific data set in any except the most facile manner. Athena is surprisingly good at not sucking at picking default values, but you should most certainly not trust the defaults blindly. She regularly chooses inappropriate values for E0, normalization, and background removal that a human operator would not choose. So feel free to poke at all those numbers on the left side of the Athena window -- that's what they are there for ;-) B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/