Signal enhancement of NMR spectra of half-integer quadrupolar nuclei in solids using hyperbolic secant pulses

Signal enhancement of the central NMR transition of quadrupolar nuclei with half-integer spin is achieved by applying a hyperbolic-secant π-inversion (sechinv) pulse to the satellite transitions. In combination with the quadrupolar Carr–Purcell Meiboom–Gill (QCPMG) pulse train, the sechinv pulse provides an additional signal enhancement of up to 2.7 for spin 3/2 nuclei in powdered solids. The 87Rb NMR enhancements realized using this experiment are compared to those obtained employing rotor-assisted population transfer (RAPT) and double frequency sweep (DFS) pulse experiments on magic angle spinning (MAS) powdered samples. In every case, the sequence employing sechinv pulses gives greater enhancements than the previously reported methods.