Multiple-pulse investigations in pure NQR spectroscopy : influence of spin-locking and phase alternated pulse sequence (PAPS) on polycrystalline samples containing 35CI (I=3/2)

The NQR responses if 35Cl (I= 3 2) in KClO3 and NaClO3 powder samples to two general categories of multiple-pulse sequences have been experimentally investigated. The sequences are: (i) spin-locking sequence (SLS), i.e. 90x-[τ-θ(X+φ)-τ]N and (ii) phase-alternated multiple-pulse sequence (PAPS), i.e. 90X-[τ-θ-X-2τ-θX-τ]N. θφ refers to an rf pulse with pulse angle θ and phase φ. SLS yields spin-locking for arbitrary θ and φ values as longas τ≤T2 and the multiple-echo decay time constant (T2ε{lunate}) for this case has been found to be much larger than the spin-spin relaxation time (T2) indicating that the resonance lines are narrowed. The observation that the spin-locking is insensitive to φ in powder specimen is a new result and cannot be explained on the basis of existing theories of multiple-pulse spin-locking in NQR spectroscopy. Line narrowing has also been observed with PAPS for arbitrary θ values and for τ values ≤ T2. T2ε{lunate} has been observed to be more sensitive to θ in this case than in the case of the spin-locking sequence.