Dear Bor-Rong Chen,

there is a very elaborated discussion of pre-edge peaks in K-edge x-ray

absorption spectra of 3d transition metal compounds:

Article Assignment of Pre-Edge Peaks in K-Edge X-ray Absorption Spec...

You may have a look into that paper. It may help you.

I will send you the full-text version via RG messenger.

Good luck

Hi Thanks for your reply! The central large peak is the "pre edge". The Mn edge is shifting and showing reduction from +7 (MnO4-, single peak pre-edge) to +4 (MnO2, double peak pre-edge).

I'm putting on a better image so that you can see the actual edge. I used Athena to normalize them.

The bump (pointed by the pink arrow) could be related to the feature of MnO4-? Throughout the literature I could not find any assignment though.

This looks a bit like the non-local excitations as described in:

https://arxiv.org/abs/0802.2744v1

and

J. Phys.: Condens. Matter 21 (2009)

and

PHYSICAL REVIEW B 77, 115133
2008

The excitations arise from metal-metal mixed orbitals mediated by O ligands. Do you have the spectra for Mn in Td with large ligands, i.e. large metal-metal distances?

Please have a look at the Farrel Lytle database (http://ixs.iit.edu/database/data/Farrel_Lytle_data/RAW/Mn/index.html), there you'll find experimental data from several different Mn-compounds, among those KMnO4 in solid and liquid form. I've plotted those data (see figure), and you'll see that the "pre-peak" is existant in both spectra, however at slightly different positions with respect to the strong prepeak related to the tetrahedral Mn7+ prepeak. So I agree with Pieter that they are probably due to the mixing of Mn orbitals with O orbitals!

Regards to all of you, Dirk

P.S. I guess it could be a good idea to look for high resolution RIXS spectra, and/or the relevant literature to clarify the origin of this peak in detail (e.g. Rev. Mod. Phys. 83 (2011) 705 , DOI: 10.1103/RevModPhys.83.705 or similar work, probably Pieter has more resources ...)