Homogeneous and inhomogeneous nuclear spin echoes in organic solids: Adamantane

Abstract

Under conditions of proton dipolar decoupling, the 13C magnetization in adamantane has been further subjected to the following separate coherent averaging procedures: magic angle mechanical spinning, Carr-Purcell, Carr-Purcell-Meiboom-Gill, and multiple-pulse (solid echo) sequences. A comparison of the respective widths of the 13C NMR response demonstrates that in adamantane the 13C 13C intermolecular dipolar coupling is approximately 40 Hz; all but the Carr-Purcell sequence reduced this, albeit with varying efficiencies. It is suggested that in an organic solid with substantial molecular motion in the kilohertz range, the 13C 13C dipolar coupling can limit spectral resolution even under magic angle sample spinning.