Correlating quadrupolar nuclear spins: a multiple-quantum NMR approach

An NMR experiment is presented which allows the relative orientation of nuclear quadrupole and dipole coupling tensors to be determined. The experiment uses a 4I quantum filter to select dipolar-coupled spin I pairs, and the relative tensor orientations are determined by lineshape analysis. One of the key features of this experiment is that because it selects dipolar-coupled spin pairs, even in a multi-spin system, it leads to data which are straightforward to interpret. The same approach is used to perform a two-dimensional correlation experiment showing which spins are close in space.