Composite sequences for efficient double-quantum Excitation over a range of spin coupling strengths

It is demonstrated theoretically and experimentally that double-quantum coherence can be excited with nearly maximal efficiency over a large range of spin coupling strengths in NMR with the use of composite excitation sequences. Such sequences are shown to be directly constructible from existing composite π 2 pulses. In addition, a general procedure is given for converting a composite excitation sequence to an equivalent, reduced form that contains fewer rf pulses and simpler rf phase shifts. Experiments are performed on the proton pair of CH₂Cl₂ oriented in a liquid crystal solvent. Applications to quadrupolar spin-1 nuclei and other dynamically simple multilevel systems are discussed.