Analysis of the performance of a phase alternated multiple pulse sequence in spin I = 7/2 zero-field NQR spectroscopy

Abstract

Zero-field nuclear magnetic resonance spectroscopy of solids containing quadrupole nuclei usually results in broad spectral lines. This line-broadening is due mainly to the inhomogeneity of the electric field gradient (EFG) at the quadrupolar nuclear site. High resolution spectra of such solids can be obtained with the application of suitably designed multiple radiofrequency (RF) pulse sequences. The performance is reported for a periodic and cyclic phase alternated multiple RF pulse sequence (PAPS) in a spin I = 7/2 system in zero external magnetic field. Average Hamiltonian theory based on the Magnus expansion is used to solve the time-dependent Liouville–von Neumann equation of motion of the spin system under the effect of the PAPS sequence. Single transition operators are employed in the spin dynamics calculations. It is shown that the multiple pulse seqeunce θ₁ - [τ - θ₂ - 2τ - θ₂ - τ] _N , where is θ₁is thw preparation pulse, suppresses the EFG inhomogeneity to a maximum extent when θ₂ = 2θ₁