Multipole N.M.R.

Using a two-spin multipole formulation, spin decoupling is analysed analytically from arbitrary initial spin preparations. The rotating frame which is most convenient is ω ≡ 1/2(ω01 + ω02) rather than the commonly used Larmor frequency of the irradiated spin ω02. The importance of unobserved polarizations (bilinear operators) is stressed by identifying these terms as providing pathways to spin coupling which must be destroyed for decoupling. Appropriate linear combinations of the bilinear polarizations can be rotated by the perturbing field. Some general observations of the effects of periodic pulse sequences and amplitude modulation are included.