Methodology for solid state NMR study of cross relaxation and molecular dynamics in heteronuclear systems

This work presents the theoretical analysis of cross-relaxation and its applications to the study of molecular dynamics in the solid state heteronuclear systems in the laboratory frame. The solid state NMR experiments were carried out on a homemade pulse spectrometer operating at the frequency of 30.2 MHz and 28.411 MHz for protons and fluorines, respectively. It is worth noting that this spectrometer includes a specially designed probe which simultaneously works at two slightly differing frequencies for protons and fluorine nuclei with complete absence of their interference. Contrary to a large number of previous cross-relaxation studies, in our experiments proton spins can be polarized in the magnetic field B0 or excited by rf pulses, while fluorine spins are continuously saturated for a long time. The saturation of fluorines is maintained throughout the whole duration of the experiment. It leads to a simplification of the mathematical analysis of the experimental results.