Dipolar coupling spin dynamics: Perturbation approach

A perturbation method is presented which can be applied to the description of a wide range of physical problems that deal with dynamics of dipolarly coupled spins in solids. The method is based on expansion of e^A+B in a perturbation series. As an example of the application of the method, the multiple-quantum coherence dynamics in three- and four-spin clusters are considered. The calculated 0Q and 2Q intensities versus the duration of the preparation period give close agreement with exact results and simulations data. The exact solutions for J_0Q and J_2Q coherences in four-spin systems are obtained.