2D OFF-RESONANCE NUTATION NQR SPECTROSCOPY OF SPIN-3 2 NUCLEI/

The effects of off-resonance irradiation in nutation NQR experiments a re demonstrated both experimentally and theoretically. The theoretical description of the off-resonance effects in 2D nutation NQR spectrosc opy is given, and general exact formulas for the asymmetry parameter a re obtained. It is shown that the outcome of the off-resonance nutatio n experiments depends on the data acquisition procedure, leading to on e- or three-line nutation spectra. To explain this fact and to describ e the off-resonance nutation experiment properly, the transient respon se theory of a quadrupolar spin system to an RF pulse was modified usi ng the wave-function approach. The 2D separation of interactions techn ique has been applied to separate a static and a randomly time-fluctua ting dynamic part of the quadrupole interaction in the antiferroelectr ic phase of polycrystalline ammonium dihydrogen arsenate. Two-dimensio nal off-resonance nutation NQR spectroscopy has been used to determine the full quadrupolar tensor of spin-3/2 nuclei in several molecular c rystals containing the Cl-35 and As-75 nuclei. The off-resonance pheno mena in 2D NQR are very important from the practical point of view (de termination of ri in multiple or broad-line spectrum) and also provide interesting information on the dynamic properties of a quadrupolar sp in system.