Aqueous ions are central to catalysis and biological function and play an important role in radiation biology as sources of damage-inducing electrons. Detailed knowledge of solute–solvent interactions is therefore crucial. For transition-metal ions, soft X-ray L-edge spectroscopy allows access to d orbitals, which are involved in chemical bonding. Using this technique, we show that the fluorescence-yield spectra of aqueous ionic species exhibit additional features compared with those of non-aqueous solvents. Some features dip below the fluorescence background of the solvent and this is rationalized by the competition between the fluorescence yields of the solute and solvent species, and between the solute radiative (fluorescence) and non-radiative channels; in particular, electron transfer to the water molecules. This method allows us to determine the nature, directionality and timescale of the electron transfer. Remarkably, we observe such features even for fully ligated metal atoms, which indicates a direct interaction with the water molecules.
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We thank F. de Groot for discussions. This work was supported by the Helmholtz-Gemeinschaft (the young investigator fund VH-NG-635), the Swiss National Science Foundation (grants 200021-116533/1 and IZK0Z2-126024) and the Swiss State Secretariat for Education and Research (COST CM0702). M.C. is grateful to the Alexander von Humboldt Foundation for support.
The authors declare no competing financial interests.
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Aziz, E., Rittmann-Frank, M., Lange, K. et al. Charge transfer to solvent identified using dark channel fluorescence-yield L-edge spectroscopy. Nature Chem 2, 853–857 (2010). https://doi.org/10.1038/nchem.768
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