Thanks, Ornella, that clarifies what you're doing. My recommendation is to look closely at the 6 reference spectra and see if there appears to be a systematic energy shift between them. For example, each spectrum might be shifted by about 0.3 eV from the spectrum before it. Or the first two spectra might appear aligned, but then the third through sixth are shifted by 1.5 eV. In either of those cases, you should align them. In my second example, I might throw out the second spectrum as an additional precaution (if the shift occurred "all at once," it might have occurred during the scan before which it appears). In either case, it doesn't really matter which scan you choose to align to (and calibrate, if you have a way of doing that). If, on the other hand, the 6 reference spectra appear to basically overplot except for random noise, I would not try to align them further. I would treat the 6 spectra for the electrolysed solution similarly-- align them to each other if there is a systematic energy shift. What you should not do, in my opinion, is to align the electrolysed scans to the reference scans. You actually expect there to be a chemical shift between the two sets of data, and aligning one to the other would remove that! --Scott Calvin Sarah Lawrence College On Oct 14, 2010, at 11:00 AM, ornella smila castro wrote:

Hi Matt and Scott,

First, thank you so much for replying to my questions. I realised that I should have been a bit more accurate on the type of experiments I am doing. To start with, I am doing electrochemistry combined with EXAFS. I am using an integrated electrolysis/EXAFS cell. Our experiments are as follow: in the case of this experiment in particular, we have a solution of ruthenium-based compound that we flow through a channel through which the beam passes and that we call "reference". we record let's say 6 spectra in a row (we use a flow in order to avoid beam damage on our sample).we didn't do any reference spectra (if you mean running a scan of a Ru foil before starting the actual experiment). then, we make up a new solution but this time we electrolysed the solution (by applying a potential) in order to get the cationic produced species. (the obtained spectra will therefore be a mixture of the neutral and the cationic species). and we record as well a set of 6 spectra. Here is what I did and what I was wondering if it was the right thing to do: I have considered the first spectra of the first set of scans as the reference for calibration/alignment. is it ok? Thus, I am wondering if when I process the second set of data (electrolysed solution), which spectra I should take as a starting point for calibrating/aligning my second series of scans: the one I used for the first serie or the first of the second set of scans?

I hope this is clear...

Thanks again for your help, Ornella