X-ray absorption fine structure (XAFS) is a powerful tool to investigate the local structure around the catalyst active site especially under the working conditions. However, it is very difficult to apply XAFS to light elements such as O, C, and N because (1) X-ray is easily absorbed by the coexisting reactant gases. (2) The XAFS signal from the light elements at the active sites is hindered by the other coexisting light elements. Here we propose a new method to identify the light element under the real catalytic conditions, called as MARX(Multi-Atom Resonant X-ray) Raman [[1]] which is a bond-specific method. The theory of MARX Raman is similar to that of MARPE(Multi-Atom Resonant Photoemission).[[2], [3]] Although there are experimental and theoretical evidence for MARPE[[4], [5]], yet many people considered it is due to the experimental artifact[[6]].
Experiment was carried out at BL36XU of SPring-8.[[7]] Figure 1 shows the C K-edge Raman signal from Er(C₅H₅)₃.[7] The excitation energy was 9752 eV just at the L1 Er edge. We found the abrupt change of emission intensity at 287 eV which was corresponding to C K-edge. It can be assigned to MARX-Raman. Theoretical investigation indicated the MARX-Raman signal was proportional to R^-2 (R was bond distance) and it appeared in the lack of spatial inversion center in the light elements. We would like to discuss the MARX-Raman possibilities though we need further experiments.

[1]Sirisit, N.et al. e-Journal Surf. Sci. Nanotechnol. 2018, 16, 387–390. https://doi.org/10.1380/ejssnt.2018.387.
[2] Kay, A. et,al. Science (80-. ). 1998, 281 (5377), 679–683.
[3] Fujikawa, T.et al.J Electron Spectrosc 2019, 233, 57-63.
[4] Yamazaki, M.; et. al., J. Phys. B At. Mol. Opt. Phys. 2007, 40 (13), F207–F213.
[5] Arai, H. et. al., J. Surf. Anal. 2008, 14 (4), 352–355.
[6] Nordlund, D. et. al., Phys. Rev. B 2001, 63 (12), 121402.
[7] Sekizawa, O. et al. SPring-8 BL36XU: J. Phys. Conf. Ser. 712, (2016).

Takashi Fujikawa

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