The shape of NMR absorption and cross-relaxation spectra in a heteronuclear spin system

A dynamic theory of heteronuclear spin systems in solids at high temperatur es is developed. A system of nonlinear integral equations for the spin time correlation functions is derived in the self-consistent fluctuating local field approximation taking into account corrections for the correlated loca l field fluctuations in real crystal lattices. The theory is applied to int erpretation of the experimental data available for a LiF crystal representi ng a system with the nuclei of two types. The signals of free precession fo r Li and F nuclei, as well as the spectra of harmonic cross-relaxation, cro ss-polarization of the Li-6 isotope, and depolarization of the Li-8 isotope , were calculated for the magnetic field oriented along the principal cryst allographic axes of LiF. The results of calculations show good agreement wi th experiment. (C) 2001 MAIK "Nauka/Interperiodica".