Enhancing the central-transition NMR signal of quadrupolar nuclei by spin population transfer using SW-FAM pulse trains with a tangent-shaped sweep profile

Solid State Nuclear Magnetic Resonance
Thomas Bräuniger

Abstract

Solid-state NMR of quadrupolar nuclei with half-integer spin, such as (25)Mg (I=5/2) or (43)Ca (I=7/2), suffers from low sensitivity, which may be improved using spin population transfer (SPT) from the satellite transitions. Effecting SPT with good efficiency is especially challenging under static conditions, and several techniques such as double-frequency sweeps (DFS), hyperbolic secant pulses (HS) and frequency-swept fast-amplitude modulated pulses (SW-FAM) have been suggested for achieving the necessary manipulations of the satellite transitions. We here investigate the SPT properties of an SW-FAM sequence with a tangent-shaped profile. The new SW(tan)-FAM pulse train is shown to possess superior SPT performance to the SW(1/τ)-FAM sequence, which hitherto has been considered to be the best FAM method for signal enhancement of static spectra, by both numerical simulations on a (27)Al model system, and experimental results on aluminium acetyl acetonate, Al(acac)(3). In addition, the CT enhancement of individual crystallites from the polycrystalline sample with a defined angle between principal z-axis of the diagonal Q-tensor and the external field was considered by numerical simulations. In the vicinity of the magic angle θ(m)...Continue Reading

References

Aug 29, 2003·Solid State Nuclear Magnetic Resonance·Hyung-Tae KwakPhilip J Grandinetti
Aug 23, 2011·Solid State Nuclear Magnetic Resonance·C Vinod ChandranThomas Bräuniger

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