A spin statistical factor in electron transfer to oxygen molecules.

Area of Science:

• Chemical kinetics
• Electron transfer reactions
• Spin chemistry

Background:

• Triplet oxygen (³O₂) is a potent electron acceptor, vital in chemical and biological processes.
• Electron transfer from spin 1/2 particles to ³O₂ can be spin-forbidden due to spin state mismatch.
• Dipole-dipole interactions in ³O₂ are proposed to facilitate spin state mixing, enabling reactions.

Purpose of the Study:

• To investigate the influence of spin effects on electron transfer to ³O₂.
• To determine how reactant diffusion coefficients impact spin selectivity.
• To elucidate the mechanisms governing spin dynamics in these reactions.

Main Methods:

• Studying electron transfer to ³O₂ across a wide range of relative diffusion coefficients (D).
• Analyzing the reaction kinetics as a function of D, spanning over three orders of magnitude.
• Correlating spin effects with diffusion rates and encounter times.

Main Results:

• Spin effects become negligible for D < 10^-9 m² s^-1.
• In intermediate diffusion regimes (10^-9 < D < 10^-8 m² s^-1), spin selectivity decreases with increasing D.
• At high diffusion rates (D > 10^-8 m² s^-1), electron transfer is spin-selective with a factor of 1/3, influenced by spin-exchange and the chemical Zeno effect.

Conclusions:

• The role of spin effects in electron transfer to ³O₂ is strongly dependent on the diffusion coefficient of the reactants.
• Encounter times exceeding spin mixing times can lead to spin-selective reactions.
• Spin-exchange interactions and the chemical Zeno effect are key factors in modulating spin dynamics within encounter complexes.