RESONANCE FREQUENCIES AND LINESHAPES OF A SYSTEM OF NUCLEI SUBJECT TO A RANDOM 2-SITE EXCHANGE

Resonance frequencies and lineshapes of a system of nuclei subject to a random two-site exchange are calculated by the second-order perturbation theory. It is assumed that the time-dependent perturbation which is the consequence of the random two-site exchange contains both diagonal and off-diagonal matrix elements in the representation of the eigenstates of the main Hamiltonian. The results show that the time-dependent perturbation averages out in two steps. A resonance line which is a doublet at very long correlation times of the random exchange changes into a singlet when τ-1cexceeds the splitting of the doublet. The second-order shift of the resonance line caused by the off-diagonal matrix elements of the perturbation vanishes when τ-1c exceeds the resonance frequencies of the main Hamiltonian. Two particular examples, NQR and quadrupole-perturbed NMR of a system of spin- 3 2 nuclei subject to a random two-site exchange, are discussed in detail. © 1993 Academic Press. All rights reserved.