Figure 10.
Principle of heteronuclear decoupling during 1H-[13C]-NMR. (A) A continuous 1H time domain signal is sampled at discrete points separated by the dwell-time Δ τ. (B) The application of short 180° pulses on the 13C channel in the middle of each dwell-time would lead to complete refocusing of heteronuclear scalar coupling evolution at each data acquisition point and to perfect decoupling. (C) RF power restrictions necessitate lengthening of the 180° 13C RF pulses over several dwell times, which would lead in the extreme case to continuous wave decoupling. (D) In order to improve the off-resonance performance, the regular 180° pulses are typically substituted with pulse combinations, composite or adiabatic RF pulses (denoted R, where the overbar represents a 180° phase inversion) and combined to form so-called decoupling super cycles.