Rotational-resonance NMR experiments in half-integer quadrupolar spin systems

Abstract

The use of rotational-resonance experiments to achieve homonuclear polarization transfer between half-integer quadrupolar spins is proposed. We give a theoretical description for a homonuclear two-spin system in the framework of Floquet theory. Numerical simulations, as well as analytical Floquet calculations, were performed to analyse the behaviour of such a system. In most cases of practical relevance, the polarization transfer between the levels involved in the central transitions of the two coupled spins can be described by a pseudo-spin-1/2 formalism. While a rotational-resonance experiment at fixed spinning speed leads only to a partial polarization transfer, an adiabatic passage through the rotational-resonance condition, achieved by a spinning-speed ramp, promotes polarization transfer for all components of the second-order quadrupolar broadened line shape.