Mechanism and kinetics of hydrated electron diffusion

Area of Science:

• Physical Chemistry
• Computational Chemistry

Background:

• The behavior of hydrated electrons is crucial for understanding various chemical and biological processes.
• Previous studies suggested specific mechanisms for electron diffusion in water, but a definitive understanding remained elusive.

Purpose of the Study:

• To elucidate the mechanism and kinetics of hydrated electron diffusion using advanced computational methods.
• To quantify the diffusion coefficient and rate constants involved in this process.

Main Methods:

• Employing molecular dynamics simulations to model hydrated electron behavior.
• Analyzing the motion of the electron's center of mass and its interaction with solvent molecules.
• Utilizing transfer diffusion models and random walk simulations.

Main Results:

• The hydrated electron exhibits Brownian-type motion with a diffusion coefficient exceeding that of the solvent.
• Electron diffusion is primarily governed by the instantaneous response to surrounding water molecule librations.
• A second-order rate constant of 5.0 ps⁻¹ was computed for electron exchange between water molecules at 298 K.
• Electron diffusion follows Arrhenius behavior from 298-400 K, with a computed activation energy of 8.9 kJ mol⁻¹.

Conclusions:

• The study confirms that hydrated electron diffusion is a transfer diffusion process involving electron exchange between neighboring water molecules.
• The computed rate constant for electron exchange accurately represents the phenomenological rate constant for diffusion.
• Findings align with and provide molecular-level insights into experimental observations.