Diffusion equation for the longitudinal spectral diffusion: the case of the RIDME experiment

Area of Science:

• Electron Paramagnetic Resonance (EPR) Spectroscopy
• Materials Science
• Physical Chemistry

Background:

• Relaxation-Induced Dipolar Modulation Enhancement (RIDME) is a technique used in EPR spectroscopy.
• Understanding proton concentration and matrix properties is crucial for various applications.

Purpose of the Study:

• To develop a simplified, diffusion equation-based analysis for RIDME time trace data.
• To enable accurate characterization of proton concentration and glassy matrices using minimal parameters.

Main Methods:

• Utilized an approximate diffusion equation-based analysis for RIDME time traces.
• Employed a global data fitting approach with only two adjustable parameters.
• Demonstrated transferability to other EPR experiments with longitudinal mixing blocks.

Main Results:

• RIDME time trace shapes showed linear scaling with proton concentration in homogeneous glassy samples.
• The two-parameter fitting approach achieved good accuracy for global data fitting.
• The fit parameters proved sensitive to the type of glassy matrix, enabling sample characterization.
• The technique is estimated to detect protons up to 3 nm from electron spins at 90% matrix deuteration.

Conclusions:

• A robust and accurate method for analyzing RIDME data has been presented.
• This technique offers a sensitive approach for structural characterization, potentially applicable in structural biology and DNP experiments.
• The developed method facilitates sample characterization based on proton concentration and matrix properties.