High-field DNP and ENDOR with a novel multiple-frequency resonance structure

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Dynamic Nuclear Polarization (DNP) and Electron Nuclear Double-Resonance (ENDOR) are crucial techniques in chemistry and physics.
• Conventional DNP and ENDOR setups face limitations in efficiency and sensitivity, particularly for low-gamma nuclei.
• Optimizing microwave cavity design is key to improving DNP and ENDOR performance.

Purpose of the Study:

• To introduce a novel triply tuned resonance structure for DNP and ENDOR experiments.
• To enhance the efficiency of radiofrequency (RF) irradiation in DNP/ENDOR.
• To improve sensitivity for low-gamma nuclei ENDOR experiments.

Main Methods:

• Development of a new resonance structure operating at 139.5 GHz electron Larmor frequency.
• Integration of the microwave cavity body as a NMR coil for simultaneous RF irradiation.
• Performance evaluation using 2H ENDOR on a perdeuterated radical and DNP experiments at 5-T fields.

Main Results:

• The novel resonator design allows the microwave cavity to function as a NMR coil, increasing RF irradiation efficiency.
• Demonstrated successful 2H ENDOR experiments on a standard radical.
• Achieved a significant 1H signal enhancement (epsilon ≈ 400 ± 50) in DNP experiments using low microwave power (17 mW).

Conclusions:

• The new triply tuned resonator offers superior performance for DNP and ENDOR compared to conventional designs.
• The design is particularly advantageous for low-gamma nuclei ENDOR due to improved sensitivity.
• Optimizing the microwave B(1) field through resonator quality factor or power level is critical for maximizing DNP signal enhancement.