Nuclear Relaxation in Coupled Spin Systems

Abstract

The density‐matrix theory of relaxation for coupled spin systems in the liquid state is reviewed and equations are derived for the calculation of nuclear Overhauser effects and free decay. The theory is applied to the results of saturation‐recovery experiments on 2,3‐dibromothiophene (CS₂ solution). The equations derived and the experimental method are in principle applicable for coupled spin systems with any number of spins. The saturation‐recovery experiment proved capable of separating the contributions of internal and external dipole interactions to the relaxation of the protons in 2,3‐dibromothiophene. The rotational correlation time for internal dipole—dipole relaxation was measured to be τ_c=(2.2±0.2)×10⁻¹² sec. The theory of correlations among the interactions of two (or more) spins with external spins is discussed. The external interactions of the two protons on 2,3‐dibromothiophene were found to be 75% correlated.