Selective on-resonance NMR irradiation of a dipolar doublet

Raman magnetic resonance where double-quantum transitions are observed with out the need for multidimensional n.m.r. spectroscopy has been investigated further. Theoretical analysis of the on-resonance case where weak continuo us-wave irradiation was applied at the frequency of a single-quantum transi tion was performed and guidelines for a consistent perturbation treatment w ere devised. Theoretical results agree well with experimental data obtained for a system of two dipolar coupled nuclei of spin 1/2 oriented by a liqui d crystal. The same approach is applicable to near-resonance experiments wh ich are shown to be the optimal experimental scheme for Raman n.m.r. By usi ng weak selective irradiation, a symmetric excitation-detection scheme can be realized for multiple-quantum n.m.r. experiments. Near- or on-resonance selective irradiation provides an efficient transfer of multiquantum cohere nce into observable coherences and could be used to study multiquantum rela xation processes.