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

Abstract

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. 90_x-[τ-θ_(X+φ)-τ]_N and (ii) phase-alternated multiple-pulse sequence (PAPS), i.e. 90_X-[τ-θ_-X-2τ-θ_X-τ]_N. θ_φ 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 (T_2ε) 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. T_2ε has been observed to be more sensitive to θ in this case than in the case of the spin-locking sequence.