The birth and evolution of solvated electrons in the water

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• Photo-induced radiolysis of water is a fundamental process in chemistry and biology.
• This process generates solvated electrons, OH radicals, and hydronium cations on ultrafast timescales.
• Understanding these dynamics is crucial for various chemical and biological reactions.

Purpose of the Study:

• To investigate the ultrafast dynamics of water radiolysis using optical-pump terahertz-probe spectroscopy.
• To characterize the transient species and solvent response following photoionization of water.
• To elucidate the structural changes in the water solvent cage around transient species.

Main Methods:

• Utilized an optical-pump terahertz-probe spectroscopy setup.
• Initiated water photoionization with ~400 nm optical laser pulses.
• Time-resolved the transient solvent response using broadband terahertz fields with ~90 fs resolution.

Main Results:

• Observed three distinct spectral responses attributed to different stages of radiolysis.
• Identified an initial short-lived, diffuse, delocalized electron with a radius of (22 ± 1) Å.
• Characterized a longer-lived intermolecular mode (150 ps) linked to solvent rearrangement around charged species.
• Detected a long-lasting negative THz band at 110 cm⁻¹, indicating a weakened hydrogen bond network in the solvent cage of the localized electron.

Conclusions:

• The study provides detailed insights into the ultrafast dynamics of water radiolysis.
• The results reveal the evolution of transient species and their interaction with the surrounding water solvent.
• The findings contribute to a deeper understanding of fundamental processes in aqueous systems.