An Updated View of Primary Ionization Processes in Polar Liquids

Area of Science:

• Physical Chemistry
• Radiation Chemistry
• Computational Chemistry

Background:

• Irradiated carbonates exhibit conflicting radical cation behavior: rapid deprotonation versus long-lived solvent-related species.
• Existing models of ionization do not fully explain these divergent observations.

Purpose of the Study:

• To reconcile conflicting data on primary radical cation behavior in irradiated carbonates.
• To develop a revised model for carbonate ionization in polar aprotic liquids.

Main Methods:

• Picosecond radiolysis and radiation-induced fluorescence spectroscopy.
• Quantum chemical calculations.
• Modeling of molecular associates in solution.

Main Results:

• Primary radical cations in irradiated carbonates are very rapidly deprotonated.
• Long-lived, solvent-related radical cationic species are also formed.
• A model based on electron loss from dimeric associates of ethylene carbonate successfully explains both phenomena.

Conclusions:

• The ionization of polar aprotic liquids like ethylene carbonate involves electron loss from molecular dimers, not isolated molecules.
• The conceptualization of primary ionization events requires revision for liquids prone to forming associates.