First Observation of Electron Transfer Mediated Decay in Aqueous Solutions: A Novel Probe of Ion Pairing

TL;DR

This paper reports the first experimental detection of electron transfer mediated decay (ETMD) in liquid water, demonstrating its potential as a sensitive probe for local chemical environments and ion pairing in aqueous solutions.

Contribution

It provides the first experimental observation of ETMD in the liquid phase and links spectral features to specific solvation structures and ion associations.

Findings

ETMD observed in aqueous LiCl solution via X-ray photoelectron spectroscopy

Spectral fingerprints differentiate water molecules and Cl- in ETMD processes

Ion pairing affects the spectral shape of ETMD signals

Abstract

A major goal of many spectroscopic techniques is to provide comprehensive information on the local chemical environment. Electron transfer mediated decay (ETMD) is a sensitive probe of the environment since it is actively involved in this non-local radiationless decay process through electron and energy transfer steps. We report the first experimental observation of ETMD in the liquid phase. Using liquid-jet X-ray photoelectron spectroscopy we explore LiCl aqueous solution, and detect low-energy electrons unambiguously emerging from the ETMD processes of core-ionized Li+. We interpret the experimental results with molecular dynamics and high-level ab initio calculations. By considering various solvation-structure models we show that both water molecules and Cl- anions can participate in ETMD, with each process having its characteristic spectral fingerprint. Different ion associations lead to different spectral shapes. The potential application of the unique sensitivity of the ETMD spectroscopy to the local hydration structure and ion pairing is discussed.