Averaging of nuclear modulation artefacts in RIDME experiments

Area of Science:

• Electron paramagnetic resonance (EPR) spectroscopy
• Pulsed EPR techniques
• Spin dynamics and relaxation

Background:

• Electron Spin Echo Envelope Modulation (ESEEM) artefacts complicate analysis in Relaxation Induced Dipolar Modulation Enhancement (RIDME) experiments.
• Accurate analysis of dipolar evolution data is crucial for understanding molecular structure and dynamics.

Purpose of the Study:

• To develop a method for removing ESEEM artefacts in RIDME experiments.
• To improve the performance of RIDME for analyzing dipolar evolution data.
• To provide analytical equations and demonstrate the applicability of the developed method.

Main Methods:

• Implementation of a refocused RIDME experiment.
• Averaging over two delay times to cancel ESEEM artefacts.
• Analytical treatment for electron and nuclear spins (S=1/2, I=1/2).
• Experimental validation using a Gd(III)-Gd(III) rigid ruler compound at Q band.

Main Results:

• Nearly quantitative removal of ESEEM artefacts was achieved by averaging over two delay times.
• The proposed method offers significantly better performance compared to existing techniques.
• Analytical equations for S=1/2, I=1/2 spin systems were derived and analyzed.
• Successful demonstration on a Gd(III)-Gd(III) system in a rigid conformation.

Conclusions:

• Averaging over two delay times is an effective strategy for ESEEM artefact removal in RIDME.
• This approach enhances the accuracy and performance of dipolar evolution measurements.
• The method is applicable to other techniques like Double Electron Electron Resonance (DEER) and Chirp-Induced Dipolar Modulation Enhancement (CIDME).