Attached is the XPS high-resolution spectrum of the N 1s region for the DPPH radical in its powder form. While analyzing the spectrum, I noticed an intense peak appearing around the 405–408 eV binding energy range. I understand that DPPH typically shows a characteristic N 1s peak, but the presence of this particular high-energy peak is quite puzzling. I’m wondering whether this could be attributed to a satellite peak, possibly due to shake-up processes or other final-state effects commonly observed in open-shell systems like radicals. Alternatively, could this peak be indicative of another nitrogen-containing species or an artefact? I’ve ruled out obvious contaminants, but the signal is quite strong, and I’m not sure how to interpret it. Has anyone encountered a similar feature in DPPH or related radical systems? I would really appreciate your insights or references. Thanks in advance!
This is the common spectral location for N in nitrates. Is there a chance that your powder contains NO3-, maybe even by decomposition?
This was commercial DPPH. I don't think the feature is due to decomposition, as the sample was not evaporated or heat-treated. The first spectrum was taken directly from the DPPH powder without any treatment. I have also attached its molecular structure and observed the same spectral features when the compound was drop-cast onto both quartz and gold substrates.
Hi Tomas,
survey spectra would be helpful as well as the information which excitation source you used, to identify possible ghost/satellite peaks.
If this can be ruled out, I agree with Jürgen that it looks like your initial DPPH already contains a significant fraction of -NO3 (for whatever reason).
Best regards
Thorsten
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