Nuclear spin relaxation and non-ergodic quasi-equilibria

For an ensemble of dipolar coupled nuclear multi-spin systems undergoing rotational diffusion the establishment of non-ergodic spin quasi-equilibria is postulated in analogy to a static powder by evaluation of the constants of the motion. While Bloch-Wangsness-Redfield relaxation theory cannot account for this phenomenon, the description of spin relaxation based on the stochastic Liouville equation shows the required quasi-equilibria.