The response of a system of spin-1 nuclei to sequences of three r.f. pulses is calculated using density matrix methods. The system is taken to be in a large but inhomogeneous B0 field and subject to both weak secular and time-dependent quadrupole couplings. Two sequences are considered, these being represented as 90° x-T-øy-T-Ɵy-t → where, for sequence I, øy=Ɵy =45oy whilst for sequence II, øy=Ɵy = = 90oy the subscripts x/y refer to axes in the usual rotating reference frame. It is shown that for both sequences, five echoes occur in phase with and following the third pulse, these occurring at times t = r, (T± t) and (2T± t). A single echo occurs at the time t=T out of phase with and following the third pulse. The dependence of the amplitudes of these echoes on t and T and the parameters characterizing the quadrupolar interactions is calculated and experiments are presented which confirm the theoretical predictions. It is shown that observation of certain of the echoes as a function of T allows the determination of individual values of the spectral densities Jq(0), Jq(wo) and jq(2wo) of the fluctuating quadrupole coupling. © Taylor & Francis Group, LLC.
