Influence of nonresonant nuclei on NMR spin echoes in liquids and in solids

Abstract

Modulations of spin echoes in liquids and echo decays in solids caused by the presence of nonresonant nuclei have been observed. General conditions for the occurrence of these effects are formulated. They involve commutation and transformation properties of various parts of the Hamiltonian and the connectivity of the transitions in the energy level diagram. The described echo modulations are due to cross terms between noncommuting homo- and heteronuclear scalar or dipolar spin couplings. Modulations of carbon-13 echoes in Carr-Purcell-Meiboom-Gill experiments in liquid malefic anhydride and echo decays in solid adamantane powder and ferrocene single crystal are described. The consequences of these modulations for various experiments utilizing echoes are discussed.