Observation of electron-transfer-mediated decay in aqueous solution


Photoionization is at the heart of X-ray photoelectron spectroscopy (XPS), which gives access to important information on a sample's local chemical environment. Local and non-local electronic decay after photoionization—in which the refilling of core holes results in electron emission from either the initially ionized species or a neighbour, respectively—have been well studied. However, electron-transfer-mediated decay (ETMD), which involves the refilling of a core hole by an electron from a neighbouring species, has not yet been observed in condensed phase. Here we report the experimental observation of ETMD in an aqueous LiCl solution by detecting characteristic secondary low-energy electrons using liquid-microjet soft XPS. Experimental results are interpreted using molecular dynamics and high-level ab initio calculations. We show that both solvent molecules and counterions participate in the ETMD processes, and different ion associations have distinctive spectral fingerprints. Furthermore, ETMD spectra are sensitive to coordination numbers, ion–solvent distances and solvent arrangement.

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Figure 1: The most relevant ETMD processes in LiCl aqueous solution.
Figure 2: Experimental and simulated ETMD spectra of LiCl aqueous solutions.
Figure 3: Radial distribution functions for LiCl aqueous solutions.


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E.M. and P.S. thank Czech Science Foundation for support (project number 13-34168S). N.V.K. and L.S.C. gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft. L.S.C also gratefully acknowledges funding from the European Research Council (Advanced Investigator Grant no. 692657). I.U., M.N.P. and B.W. gratefully acknowledge support from the Deutsche Forschungsgemeinschaft (DFG Research Unit FOR 1789). The authors thank the BESSY II staff for assistance during the beamtimes. We thank E. Pluhařová for valuable discussions.

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I.U., R.S., S.T., M.N.P. and B.W. conceived, designed and performed the experiments, and analysed the experimental data. E.M. and P.S. performed and analysed the molecular dynamics simulations. N.V.K. computed the theoretical ETMD spectra and analysed them. B.W., P.S. and N.V.K. co-wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Petr Slavíček or Bernd Winter or Nikolai V. Kryzhevoi.

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The authors declare no competing financial interests.

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Unger, I., Seidel, R., Thürmer, S. et al. Observation of electron-transfer-mediated decay in aqueous solution. Nature Chem 9, 708–714 (2017). https://doi.org/10.1038/nchem.2727

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