Two-dimensional RF pulses: A new approach to selectively exciting J-coupled spins in nuclear magnetic resonance

A new scheme for the excitation of spins according to the joint values of their heteronuclear or homonuclear J couplings and of their chemical shifts, is proposed and demonstrated. The principles of the new pulses involved derive from those employed in NMR imaging for exciting arbitrary 2D spatial shapes, using so-called "multidimensional" RF pulses. It is shown that if recast in a suitable spectroscopic framework, the distinction that π-pulses enable to establish between linear and bilinear interactions, support the selective excitation of coherences possessing arbitrary combinations of chemical shift and J-coupling values - a flexibility akin to that provided by a 2D J-resolved NMR spectrum. Details on the execution of the resulting 2D "J-shift" RF pulses are given, and examples where excitation only addresses spins with particular chemical shift offsets fulfilling specific J-coupling displacements, are demonstrated. Additional instances where such pulses could be applied, as well as main limitations of this new approach, are briefly discussed.