Cations strongly reduce electron-hopping rates in aqueous solutions

Area of Science:

• Physical Chemistry
• Chemical Physics
• Materials Science

Background:

• Ultrafast electron hopping is crucial for charge transfer in aqueous systems.
• The influence of the local molecular environment on electron hopping dynamics is not fully understood.

Purpose of the Study:

• To investigate how the local molecular environment affects ultrafast electron hopping.
• To determine the impact of atomic ions on electron hopping rates in liquid water.

Main Methods:

• Resonant Auger decay spectroscopy of water O1s core holes.
• Analysis of electron hopping times in neat water and electrolyte solutions (LiBr, MgBr2).
• Density functional theory (DFT) calculations and molecular dynamics (MD) simulations.

Main Results:

• Electron hopping rates are significantly reduced when water molecules are replaced by ions.
• Electron hopping times increase in electrolyte solutions (e.g., 1.5 fs in 6 m LiBr, 1.9 fs in 3 m MgBr2) compared to neat water (∼3.6 fs).
• Hopping rate shows a strong dependence on cation charge, attributed to ion-induced reduction of water-water orbital mixing.

Conclusions:

• The local ionic environment can deliberately manipulate ultrafast electron hopping rates in aqueous media.
• Electrostatic perturbations by solvated ions alter water-water orbital mixing, affecting electron transfer.
• This work provides a pathway to control charge transfer dynamics in solutions.