Calculation of cross-polarization spectra influenced by slow molecular tumbling

A numeric algorithm which is suitable for calculating lineshapes of cross-polarization spectra influenced by isotropic and anisotropic tumbling is proposed. It is based on a description of the cross-polarization process using single-transition operators combined with rotational diffusion represented by a stationary Markov operator. A corresponding Fortran program can be implemented on a regular personal computer. The calculations yield spectral lineshapes for various mixing times under given cross-polarization conditions which reflect the characteristics of molecular motion. Representative results show typical transient oscillations on powder spectra, the dependence of the lineshapes on the degree of mobility, the effects of sample spinning, the consequence of a given deviation from the Hartmann-Hahn condition, and the effect of additional dipolar coupling between I spins. The applicability of the algorithm is demonstrated on supercooled glycerol as a model system. Copyright 2000 Academic Press.