Design of heteronuclear decoupling sequences for solids

Abstract

A strategy of designing new heteronuclear broadband decoupling sequences for solid state NMR is presented. From a semiquantitative analysis of the problem, it is concluded that the use of multifrequency excitation in the rotating frame would lead to an effective averaging of the heteronuclear dipolar interaction. The actual implementation involves a phase modulation of the decoupler as a function that is a sum of several cosine terms. The new decoupling sequences are abbreviated as CPM m-n for cosine phase modulation with m harmonics and having frequency intervals of ωrf/n, where m and n are integers. Experimental results show that their performances are considerably better than those of the existing decoupling methods, under conditions of moderate spinning rate and decoupling power.