Chirp echo Fourier transform EPR-detected NMR

Area of Science:

• Magnetic Resonance Spectroscopy
• Quantum Electronics
• Physical Chemistry

Background:

• Electron Paramagnetic Resonance (EPR) spectroscopy is crucial for studying paramagnetic centers.
• Existing methods like FT EPR-detected NMR and ELDOR-detected NMR provide valuable information but have limitations.
• There is a need for more efficient and comprehensive techniques for nuclear frequency analysis in EPR.

Purpose of the Study:

• Introduce a new ultra-wide band (UWB) pulse EPR method for single-shot observation of all nuclear frequencies.
• Develop a technique that offers multiplex advantages over existing EPR-detected NMR methods.
• Demonstrate the applicability of the new method for analyzing hyperfine interactions and nuclear couplings.

Main Methods:

• Implementation of Chirp Echo EPR Spectroscopy (CHEESY)-detected NMR.
• Utilizing a high turning angle (HTA) pulse to excite forbidden transitions and burn spectral holes.
• Detection of the hole pattern using a chirp echo, analogous to Fourier Transform (FT) EPR-detected NMR.
• Application of selective pulses to probe hyperfine sublevel correlations.

Main Results:

• Successfully observed all nuclear frequencies of a paramagnetic center in a single shot using CHEESY-detected NMR.
• Obtained spectra comparable to ELDOR-detected NMR but with enhanced efficiency (multiplex advantage).
• Correlated hyperfine spectra with EPR spectra by varying HTA pulse frequency in nitroxides.
• Elucidated nuclear coupling regimes and hyperfine sublevel correlations in hexaaquamanganese(II), similar to HYSCORE experiments.

Conclusions:

• CHEESY-detected NMR is a powerful revival of FT EPR-detected NMR, offering significant advantages.
• The method is effective for analyzing hyperfine interactions and nuclear couplings in paramagnetic systems.
• The technique is expected to be broadly applicable to disordered systems and motivates the development of advanced EPR spectrometers.