Effects of Perturbing Radiofrequency Fields on Nuclear Spin Coupling

An analysis is made of double resonance experiments in which the ${\mathbf{I}}_1$·${\mathbf{I}}_2$ interaction observable in certain nuclear magnetic resonance spectra is perturbed by a strong radiofrequency field. The problem is treated by transforming to a rotating coordinate system in which all terms in the Hamiltonian are stationary except for the weak rf field used to investigate the spectrum. Transition energies and intensities are computed in the rotating frame and the spectrum transformed back to the laboratory frame by adding a constant factor to the energy. A double-resonance experiment involving the nuclei ${\mathrm{F}}^{19}$ and ${\mathrm{P}}^{31}$ is described and the experimental results compared with those computed from the theory.