Issue 15, 2022

Probing aqueous ions with non-local Auger relaxation


Non-local analogues of Auger decay are increasingly recognized as important relaxation processes in the condensed phase. Here, we explore non-local autoionization, specifically Intermolecular Coulombic Decay (ICD), of a series of aqueous-phase isoelectronic cations following 1s core-level ionization. In particular, we focus on Na+, Mg2+, and Al3+ ions. We unambiguously identify the ICD contribution to the K-edge Auger spectrum. The different strength of the ion–water interactions is manifested by varying intensities of the respective signals: the ICD signal intensity is greatest for the Al3+ case, weaker for Mg2+, and absent for weakly-solvent-bound Na+. With the assistance of ab initio calculations and molecular dynamics simulations, we provide a microscopic understanding of the non-local decay processes. We assign the ICD signals to decay processes ending in two-hole states, delocalized between the central ion and neighbouring water. Importantly, these processes are shown to be highly selective with respect to the promoted water solvent ionization channels. Furthermore, using a core-hole-clock analysis, the associated ICD timescales are estimated to be around 76 fs for Mg2+ and 34 fs for Al3+. Building on these results, we argue that Auger and ICD spectroscopy represents a unique tool for the exploration of intra- and inter-molecular structure in the liquid phase, simultaneously providing both structural and electronic information.

Graphical abstract: Probing aqueous ions with non-local Auger relaxation

Supplementary files

Article information

Article type
14 Jan 2022
22 Mar 2022
First published
23 Mar 2022
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2022,24, 8661-8671

Probing aqueous ions with non-local Auger relaxation

G. Gopakumar, E. Muchová, I. Unger, S. Malerz, F. Trinter, G. Öhrwall, F. Lipparini, B. Mennucci, D. Céolin, C. Caleman, I. Wilkinson, B. Winter, P. Slavíček, U. Hergenhahn and O. Björneholm, Phys. Chem. Chem. Phys., 2022, 24, 8661 DOI: 10.1039/D2CP00227B

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