On Monday 14 November 2005 14:24, Peter Leinweber wrote:
dear all, i am a new XANES and ATHENA user. i didi N K-edge XANES of soil samples. while feeling very good with data import, deglitching, truncation, merging etc. i am insecure about parameters for normalization. in the attached project i did truncation of data before 395900 (it is milli-eV), because these seem to be invalid, and i set an E-shift of -900 sinc the beamline had -9.9 eV off compared to the N K-edge of N2 gas. in this way i should be right back on scale ? the i did set the pre-edge parameters manually at start of the curve, and around 397000 since non of the previously measured N standard substances had edge steps below this value. however, then i am insecure how to set the other parameters for normalization properly. depending on how i play with the parameters sometimes i get normalized spectra which look pretty reasonable, sometimes the curves disappear completely from the graphics window, and sometimes i get curves of a shape never senn in the literature. is there easily understandable advice for the setting of the normalization parameters available; or can anybody more experienced check my project and give me recommendations.
Hi Peter, I didn't write Athena thinking about this energy range, so you are certainly looking at some of its rough edges. First off, Athena's unit of currency is eV. Your data seems to be in meV. Background removal is certainly not going to work correctly. Other features of the program might also make certain assumptions about the data being in eV units. One thing you might do to make the program behave less confusingly might be to convert the data files to eV before reading them into Athena. If you must treat the data in meV, then I would suggest reading them in as xanes(E) data rather than mu(E) data. This will turn off the background removal, which is likely to be the most confused part of the program by the meV units. This can be done in the column selection dialog or by selecting "Change record type" from the Group menu. Background weirdness due the meV units seems the most likely reason that the curves might disappear completely from view. I got a fairly reasonable normalization using your eO and [-3695:1910] for the pre-edge range and [3062:10200] for the normalization range. I just chose values using the little blue pluck buttons which seemed to be in a range that would reasonably represent the pre- and post-edge regions. In general normalization is kind of tough for these low energy edges. Using the CLnorm option which Ifeffit/Athena provides might be useful, but the data *must* be in eV units for that to work. B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advance 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/