PHASE-MODULATED NUTATION NUCLEAR-QUADRUPOLE RESONANCE SPECTROSCOPY

Nutation nuclear quadrupole resonance spectroscopy enables one to dete rmine the asymmetry parameter on powder samples. The method relies on two-dimensional methodology: The first period is the duration of the r adio frequency exciting pulse and the second dimension is the free-evo lution period of the quadrupolar nucleus. Varying lengths of the radio frequency pulse induce an amplitude modulation of the free-induction decay signals which is characteristic of the anisotropic nutation freq uency distribution. Fourier analysis along the first dimension provide s a powder nutation line shape that allows determination of the electr ic field gradient tenser's asymmetry parameter. We describe the first application of two-dimensional phase-modulated spectroscopy to a quadr upolar nucleus at zero field. It is shown that a phase-modulated varia nt of the nutation spectroscopy is feasible in the pure quadrupole reg ime and it provides a gain in the signal-to-noise ratio compared to th e amplitude-modulated method. (C) 1998 American Institute of Physics.