Limits to resolution in multiple-pulse NMR

Abstract

An experimental and theoretical account is presented of various multiple-pulse experiments in solids based on cycles using reflection symmetry. The line-narrowing efficiency or spectral resolution of these cycles depends critically on the residual terms in the effective Hamiltonian. We identify three resonance-offset-dependent line-broadening mechanisms. Several new pulse sequences which reduce the broadening caused by these sources are demonstrated. The spectrometer alignment procedure for multiple-pulse sequences is described in detail and the effect of a particular phase-alignment error on line-narrowing efficiency is discussed.