| Résumé | We present the first 14N overtone NMR spectra obtained directly under magic angle spinning conditions. Line-broadening contributions from chemical shift anisotropy and heteronuclear dipolar couplings are significantly reduced, and, despite theoretical predictions, spinning sidebands are minimal, leaving second-order quadrupolar powder patterns with narrow discontinuities that can be observed using a single excitation pulse. We also show that the limited bandwidth and offset-dependent nutation rates exhibited by standard RF pulses can be overcome using frequency-swept pulses, allowing the direct acquisition of solid-state 14N NMR spectra in which multiple nitrogen sites are well-resolved. |
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