Isotropic solid-state MQMAS NMR spectra for large quadrupolar interactions using satellite-transition selective...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Quantum Coherence Manipulation

Background:

• Multiple-quantum magic-angle spinning (MQMAS) is crucial for obtaining isotropic NMR spectra.
• Large quadrupolar interactions in nuclei pose challenges for traditional MQMAS experiments.
• High radiofrequency (rf) fields are typically required, limiting applicability.

Purpose of the Study:

• To develop novel MQMAS pulse sequences requiring lower rf fields.
• To enable high-resolution NMR analysis of systems with large quadrupolar interactions.
• To improve the efficiency and accessibility of MQMAS for challenging materials.

Main Methods:

• Design and implementation of low-power multiple-quantum magic-angle spinning (lpMQMAS) pulse sequences.
• Utilizing rotor-period long pulses with large offset from the central-transition for satellite-transition selectivity.
• Employing symmetric pulse pairs to cancel anisotropic phases and achieve coherent evolution.
• Selective inversion of satellite-transitions to efficiently excite and convert triple-quantum coherences.

Main Results:

• Demonstrated successful application of lpMQMAS sequences on RbNO3 and β-Ga2O3.
• Obtained isotropic NMR spectra for samples with significant quadrupolar couplings.
• Achieved efficient excitation and coherence transfer using low-power pulses.
• β-Ga2O3, exhibiting the largest quadrupolar interactions to date, yielded interpretable isotropic NMR spectra.

Conclusions:

• lpMQMAS pulse sequences effectively overcome limitations of high rf power requirements.
• These sequences provide a viable method for analyzing materials with large quadrupolar interactions.
• The demonstrated lpMQMAS technique broadens the scope of high-resolution solid-state NMR analysis.