Site- and Energy-Selective Low-Energy Electron Emission by X-rays in the Aqueous Phase

Low-energy-electron emission from resonant Auger final states via intermolecular Coulombic decay (RA-ICD) has previously been described as a promising scenario for controlling radiation damage for medical purposes, but it has so far only been observed in prototypical atomic and molecular van der Waals dimers and clusters. Here, we report the experimental observation of RA-ICD in an aqueous solution. We show that for solvated Ca²⁺ ions, the emission can be very efficiently controlled by tuning the photon energy of exciting X-rays to inner-shell resonances of the ions. Our results provide the next step from demonstrating RA-ICD in relatively simple prototype systems to understanding the relevance and potential applications of ICD in real-life scenarios.