Rotational echo double resonance in ISN spin networks:: Deconvolution of multiple dipole-dipole couplings

In a recent paper we have demonstrated how a simple modification to the standard rotational echo double resonance pulse sequence, where the flip angle of the pulse applied to the S spin is varied, can be used to separate the measurement of the magnitude of I-S dipole-dipole couplings from that of their relative orientation. An equivalent result can be achieved via phase modulation which labels and differentiates between different evolving coherences in the density matrix based on the number of S spins participating-exactly as is done in multiple quantum spectroscopy. As phase modulation can be effected on modern instruments with much higher precision, in this paper we explore the experimental implementation of this method in the IS2 spin system glycine-C-13(2)-N-15, and discuss generalizations of this technique to larger spin systems. (C) 2001 American Institute of Physics.