OFF-RESONANCE NUTATION NMR-SPECTROSCOPY OF HALF-INTEGER QUADRUPOLAR NUCLEI

The possibilities of off-resonance irradiation in nutation experiments of half-integer quadrupolar nuclei are demonstrated experimentally and theoretically. Off-resonance irradiation extends the applicability of nutation NMR spectroscopy at a given radiofrequency field strength to a larger range of quadrupole coupling constants. Moreover, it is possible to obtain several spectra with different resonance offsets on one spectrometer, thus facilitating the determination of the quadrupole parameters. A loss of signal to the uninformative zero-frequency signal which accompanies off-resonance irradiation can be avoided by using a frequency-stepped adiabatic half-passage or a soft selective 90° pulse as preparation for the experiment. Simulated off-resonance nutation spectra are presented as a function of quadrupole coupling constant and resonance offsets. The technique is demonstrated experimentally for a number of sodium compounds. © 1993 Academic Press. All rights reserved.