14N magic angle spinning overtone NMR spectra

We present the first N-14 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 N-14 NMR spectra in which multiple nitrogen sites are well-resolved. Crown Copyright (C) 2011 Published by Elsevier B. V. All rights reserved.