GENERAL THEORETICAL FORMALISM FOR DESCRIBING THE HIGH-ORDER EFFECTS OF THE DIPOLAR COUPLING BETWEEN SPIN-1 2 AND QUADRUPOLE NUCLEI/

A general theoretical description of the effect of the second-order di polar coupling between spin-1/2 and quadrupole nuclei is presented bas ed on the density operator formalism rather than the Shrodinger equati on as in previous publications. The main task of this formalism is to diagonalize the evolution operator which can be performed analytically when the quadrupole nucleus is spin-1 or spin-3/2; no approximations such as the adiabatic assumption, perturbation expansion and the avera ge Hamiltonian treatment are assumed. Therefore, it is general and can be used for all nuclear spins and any value quadrupole coupling const ant and in the case of magic-angle spinning (MAS) for any rotor spinni ng speed; it can also include the case when more than one species of s pin-1/2 nuclei is coupled to the quadrupole nucleus. The effects of in direct dipolar coupling, chemical shift anisotropy and sample spinning speeds on Nuclear Magnetic Resonance (NMR) lineshapes can be uniforml y incorporated in the formalism. Lineshape simulations based on this f ormalism can yield structural and electronic parameters of compounds a nd materials with high accuracy. Experimental results for several typi cal compounds of different complexities are demonstrated and are shown to be in good agreement with the theoretical spectral simulations. (C ) 1997 American Institute of Physics.