Two-dimensional lineshapes

An important shortcoming of the two-pulse methods is the difficulty of balancing the echo and antiecho amplitudes to obtain undistorted two-dimensional lineshapes, especially for nuclei with spin larger than 3/2. The two coherence-transfer pathways being different, it has been shown that their amplitude depends on the quadrupole couphng and the orientation of the crystallites. In a powder, it is nearly impossible to reach a perfect equalisation of these amplitudes. 

---