THE DETECTION OF WEAK HETERONUCLEAR COUPLING BETWEEN SPIN-1 AND SPIN-1/2 NUCLEI IN MAS NMR - N-14/C-13/H-1 TRIPLE RESONANCE EXPERIMENTS

Magic angle spinning and N-14 irradiation have been employed to perturb the N-14 spin bath, in a new spin-echo triple resonance solid-state NMR experiment. Spinning introduces a time dependence in the N-14 quadrupolar interaction, permitting transitions between the three \I, m > states, two or four times per rotor cycle; this alters the evolution of a N-14-coupled C-13 spin. The reduction in C-13 echo intensity, on N-14 irradiation during the echo period, is greater for shorter C-N distances. Irradiation at a constant frequency is more effective than sweeping through the N-14 resonance. N-14 double-quantum spectra are obtained indirectly by irradiation of the double-quantum transition.