Hi Francesco, This showed up while I was on vacation and it seems not to have gotten an answer. I'll give it a shot. I think the most correct answer to your question would rely upon Fourier analysis. If you remove from the data a number of points whose width is small compared to the wavelengths of the portion of the data that you are attempting to analyze, then you are probably safe. When the software moves the data from mu(E) to chi(k) after background removal, it interpolates the data onto the "standard" k grid, which is even spaced with points separated by 0.05 invAng. This interpolation grid is very fine compared to the frquencies of the data you will ever analyze. When you deglitch, the points are removed, then the background is removed, then the interpolation happens. If the width of the region removed by deglitching is wide enough, then the interpolation will necessarily change the Fourier spectrum. If it is narrow enough, then the interpolation will be a reliable approximation of the true data. In your specific case, 1 and 2 point glitches are almost certainly safe to remove. A 10 point glitch is probably not safe to remove. I am not going to commit to rule of thumb, however... :P B On 06/29/2015 03:41 PM, Francesco Marafatto wrote:

Hello All,

I have enjoyed this digest in the past and found it very helpful! I hope it may provide an answer to my question.

I am collecting Mn EXAFS data out to k of 15 Å-1, and the data look fine. However, the monochromator (Si 111) has 5 strong 2-point glitches and 3 minor 1-point glitches in one of the regions that I am most interested in (k between 5 and 9 Å-1).

My question relates to how many data points I can remove before influencing the data. In my previous experience I have removed 2 or 3 points but never more. I have read through the deglitching section of “XAFS for Everyone”, and think that I could oversample the EXAFS (with k steps of 0.03 Å-1 vs 0.05 Å-1), but most of the data have already been collected. Is there a rule of thumb about deglitching? In other words, is there a limit to the number of bad points I can eliminate for an EXAFS scan to k of 15 Å-1?

Thanks and looking forward to hearing your thoughts,

Francesco

Francesco Femi Marafatto francesco.marafatto@unil.ch FNS PhD student, Environmental Geochemistry Laboratory IDyST - FGSE Bureau 3233 Gèopolis Université de Lausanne CH-1015 Lausanne T. +41 (0)21 692 4451

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