Behaviour of a coupled two-spin-1/2 system in the presence of a spin-locking radio-frequency field. Relaxation and Hartmann-Hahn transfers

Abstract

The theory of the evolution of a J-coupled homonuclear system of two nuclei of spin 1/2 (in the liquid state) subjected to a spin-locking field is explicitly reformulated in terms of simultaneous differential equations. Quantities destroyed by the inhomogeneity of the spin-locking field are delineated; from these considerations it is found that only four quantities interfere: the two transverse magnetizations of concern (supposed to be in absorption), one observable mode corresponding to the difference of antiphase dispersive doublets and one mode (unobservable) involving zero/double quantum coherences. Transfers of Hartmann-Hahn type occur necessarily via the antiphase doublet mode. Analytical solutions could be derived for these transfers, which occur in an oscillatory fashion. The frequency of the Hartmann-Hahn oscillations is shown to depend not only upon J but also upon the characteristics of the spin-locking field (amplitude and offset with respect to the resonance frequencies of the two nuclei). Wh...