The NMR of quadrupolar nuclei. Relationship between exact and perturbation solutions for spin 3/2

► Simple and direct derivation of second-order perturbation effects. ► Clear physical picture of how the coherences interact. ► A direct method: no need to calculate wavefunctions or Hamiltonians. ► No commutators of operators, just simple matrix elements with explicit formulae. ► Easily adapted to computer algebra or numerical calculations.