# Non-local X-ray intermolecular radiative decay probes solvation shell of ions in water

## TL;DR

This paper introduces a new X-ray technique to study how water molecules surround ions like Na+ and Mg2+ in water.

## Contribution

The study demonstrates a novel non-local X-ray emission process to selectively probe the solvation shell of ions in water.

## Key findings

- Intermolecular Radiative Decay involves an electron from the solvation shell filling a core hole in the ion.
- The emitted X-ray photon provides information about the solvation shell's electronic and geometric structure.

## Abstract

Aqueous solutions are crucial in chemistry, biology, environmental science, and technology. The chemistry of solutes is influenced by the surrounding solvation shell of water molecules, which have different chemical properties than bulk water due to their different electronic and geometric structure. It is experimentally challenging to selectively investigate this property-determining electronic and geometric structure. Here, we report experimental results on the non-local X-ray emission process Intermolecular Radiative Decay, for the prototypical ions Na+ and Mg2+ in water. We show that, in Intermolecular Radiative Decay, an electron from the solvation shell fills a core hole in the solute, and the released energy is emitted as an X-ray photon. We interpret the underlying mechanism using theoretical calculations, and show how Intermolecular Radiative Decay will allow us to meet the challenge of selectively probing the solvation shell from within.

Core ionization of ions in solution leads to decay processes involving interaction with the environment. Here, the authors report a non-local X-ray emission process in core-ionized Na+ and Mg2+ that can be used to probe the ions’ solvation shells.