EPR Spectra and Electron Spin Relaxation of O₂

Area of Science:

• Physical Chemistry
• Biophysics
• Spectroscopy

Background:

• Collisions with oxygen (O2) broaden electron paramagnetic resonance (EPR) spectra of free radicals, a phenomenon known since the 1950s.
• The effect of O2 on EPR spectra and relaxation times has been utilized for in vivo oxygen concentration measurements.
• Existing literature focuses on O2 sensing using various radicals and particles, assuming short O2 electron spin relaxation times.

Purpose of the Study:

• To provide a comprehensive review of the EPR spectra and electron spin relaxation of O2.
• To consolidate existing literature on O2's interaction with EPR spectroscopy.
• To serve as a resource for the O2 measurement community, particularly for in vivo applications.

Main Methods:

• Literature review of pioneering and contemporary studies on O2 and EPR.
• Analysis of the effect of O2 on continuous wave (CW) EPR spectra.
• Examination of O2's influence on electron spin relaxation times in different phases.

Main Results:

• O2 significantly broadens EPR spectra of free radicals in fluid solutions.
• O2's effect on relaxation times is crucial for accurate in vivo O2 measurements.
• A gap exists in the literature regarding a consolidated review of O2's EPR properties across gas, fluid, and frozen states.

Conclusions:

• Understanding O2's EPR characteristics is vital for advancing in vivo oxygen sensing technologies.
• This review synthesizes key findings on O2's spectral broadening and relaxation effects.
• The presented summary aims to facilitate further research and application development in O2 measurements using EPR.