Transfer of coherence and effect of level shift caused by two-quantum excitation in a multilevel NMR system

The phenomenon of transfer of coherence and the effect of level shift caused by two-quantum (TQ) excitation were studied on ²⁷Al nuclei in Al₂{O}₃$. Transfer of coherence between two single-quantum (SQ) transitions and that between SQ and three-quantum transitions were examined. It was observed that the coherences transfer periodically with frequency equal to one-half the TQ transient nutation frequency accompanied by phase shifts caused by the level shift. Experimental results are in good agreement with theoretical predictions. The effect of magnetic dipole interaction was also studied. A precise measurement was made on the shift of TQ resonance frequency and it was confirmed that no shift exists on the TQ resonance frequency contrary to the prediction based on the three-level model.