Double-Quantum Filtered —H COSY

In the description of the 2-D experiment above for an AX spin system, we found that during tx spins, which 

Before undertaking detailed discussions of H— H COSY and the structure of ipsenol, there is one further refinement that decreases the clutter along the diagonal. Although we can interpret this spectrum without this refinement, there are instances (e.g., caryophyllene oxide) when this improvement makes a great deal of difference. 

By simply adding a third ir/2 pulse immediately following the second W2 pulse in our simple COSY pulse sequence and changing nothing else, we have the pulse 

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