RAPID MEASUREMENT OF NUTATION NQR SPECTRA IN POWDERS USING AN RF PULSE-TRAIN

The method of two-dimensional nutation NQR spectroscopy, introduced by Harbison in 1989, has been successfully used for determining of the a symmetry parameter of the EFG tensor for spin-3/2 nuclei in both powde red and monocrystal samples in the absence of an external magnetic fie ld. The inconvenience inherent in the method, however, is the long tim e required, because data acquisition must be repeated for various RF p ulse lengths. We discuss a method to reduce the time of the nutation e xperiment by using a sequence of identical short RF pulses of length t (w) and distance tau. It is shown that for an NQR frequency omega(0), frequency offset Delta omega, and pulse parameters satisfying the rela tion omega 0 tau + Delta omega t(w) = 2 pi k (k = 1, 2, 3,..., n) a sy nchronism of pulse action takes place and the nutation interferogram c an be measured ''stroboscopically'' between the pulses. The maximum ti me saving factor that can be obtained as compared to the conventional nutation experiment is of the order of the number of pulses used in a pulse train. The method has been successfully applied for determinatio n of the asymmetry parameter for one of the two Cl-35 sites in polycry stalline 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride).