Phase-alternated composite pulses for zero-field NMR spectroscopy of spin 1 systems

Abstract

A set of composite pulses is described that compensates the effects of electric field gradient (EFG) inhomogeneity and resonance offset for zero-field NMR spectroscopy of a single crystal specimen containing physically equivalent spin 1 nuclei. These sequences are designed using the Magnus expansion approach. The phases of the RF pulses in the sequence are restricted to 0 and 180 only. The phase restriction drastically reduces the complexity and computation time involved in the numerical search of composite pulses via the Magnus expansion method. The derivation of phase-alternating composite pulses and the computer simulations which describe their performance against offset and EFG inhomogeneity effects are presented. It is inferred that the performance of these composite pulses is symmetric with respect to the sign of the offset and independent of asymmetry in EFG tensor. Based on these, a 45 135, composite π/2 pulse, and a 315 225 90, broadband population inversion pulse, are proposed for the zero-field NMR spectroscopy of solids. Composite pulses reported here are applicable also to the high field NMR spectroscopy of spin ½ nuclei.