Phase Cycling and Coherence Transfer Pathways

The transitions between energy levels in an AX spin system are shown in Fig. 1.44. There are four single-quantum transitions (these are the normal transitions A, Aj, X, and in which changes in quantum number of 1 occur), one double-quantum transition between the aa and /3/3 states involving a change in quantum number of 2, and a zero-quantum transition VVo between the a/3 and /3a states in which no change in quantum number occurs. The double-quantum and zero-quantum transidons are not allowed as excitation processes under the quantum mechanical selection rules, but their involvement may be considered in relaxation processes. 

Transverse magnetization represents a particular type of coherence involving a change in quantum number p of 1. Each coherence ct is equal to the difference in magnetic quantum numbers of the nuclei r and s, i.e., the coherence order is and pulses cause transitions to occur 

Suppose the first pulse resulted in the creation of a phase coherence across the A transition between the aa and a)8 states (Fig. 1.44). It is possible to transfer this phase information from the a/3 state to the /3/3 state by applying a selective n pulse across the Xi transition. The two successive pulses would therefore transfer the phase of the aa state to the )8/3 state, with the two states now becoming phase coherent with one another. 

Apparently, all coherence pathways will therefore start at zero coherence levels and end at -(-1 coherence levels since the quadrature receiver is sensitive only to the -t-1 polarization, only the single-quantum coherence is detected. 

Summarize the different events during a pulsed NMR experiment, 

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