Effect of relaxation on the nuclear double resonance spectra of weakly coupled spin systems; proton double resonance in ethyl fluoride

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Abstract
The density-matrix method of analysing relaxation effects in nuclear magnetic double resonance experiments is extended to the case of large molecules containing several groups of equivalent nuclei giving rise to fist-order single resonance spectra. The difficulty of using this theory for such systems possessing degenerate energy levels is circumvented by assuming that the relaxation in the system occurs through an istropic random field with complete correlation between interactions within each group and no correlation between interactions with different groups. This relaxation mechanism preserves the equivalence of the spins in each group signified by the spin Hamiltonian. This assumption, along with those used in the general theory, not only permits, in suitable cases, the use of a convenient approximation originally proposed by Bloch for simplifying the computations involved in the theory, but also separates the problem into a linear superposition of several independent sub-problems of much smaller dimension. The method is applied to proton double resonance experiments in C2H5F, which show some features arising from relaxation in the system. It is estimated from the analysis that the spin relaxation of fluorine in C2H5F is about four times as efficient as that of the protons.

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