Probing aqueous ions with non-local Auger relaxation

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Surface Science

Background:

• Non-local relaxation processes, such as Intermolecular Coulombic Decay (ICD), are crucial for understanding condensed-phase dynamics.
• Isoelectronic cations in aqueous solutions provide a model system to study these decay mechanisms.

Purpose of the Study:

• To investigate Intermolecular Coulombic Decay (ICD) in aqueous-phase isoelectronic cations (Na+, Mg2+, Al3+) following 1s core-level ionization.
• To elucidate the role of ion-water interactions in modulating ICD processes and timescales.
• To explore the potential of Auger and ICD spectroscopy for analyzing liquid-phase structures.

Main Methods:

• K-edge Auger spectroscopy was employed to detect ICD signals.
• Ab initio calculations and molecular dynamics simulations were used for microscopic analysis.
• Core-hole-clock analysis was applied to estimate ICD timescales.

Main Results:

• ICD signals were unambiguously identified in the K-edge Auger spectra of Mg2+ and Al3+.
• ICD signal intensity correlated with ion-water interaction strength, being highest for Al3+ and absent for Na+.
• Decay processes were assigned to two-hole states delocalized between the ion and surrounding water molecules.
• ICD timescales were estimated at ~76 fs for Mg2+ and ~34 fs for Al3+.
• ICD processes demonstrated high selectivity towards specific water solvent ionization channels.

Conclusions:

• Auger and ICD spectroscopy offer a powerful method for probing intra- and inter-molecular structures in liquids.
• These techniques provide simultaneous structural and electronic information.
• The study highlights the importance of non-local decay processes in condensed-phase systems.