CALCULATION OF NMR FREE INDUCTION SIGNALS FOR NUCLEI OF MOLECULES IN A HIGHLY VISCOUS MEDIUM OR A SOLID-LIQUID SYSTEM

A general solution of the Isotropie rotational diffusion equation applied to NMR transverse magnetization of molecules containing two identical spin-one-half nuclei is used to obtain the spin-echo amplitudes in one, two, and multiple 90° pulse sequences. Numerical calculations using the rotational correlation times (or rotational diffusion coefficients) appropriate to a highly viscous medium are used to evaluate the observable NMR decay parameters (T 2* and T3*). For rapid motion this general calculation gives the well-known results for secular contributions to transverse relaxation. In the limit of slow motion, the shape parameter (B T 3*) of the spin-echo amplitude at 2τ is found to depend on the cube root of the product of the splitting constant (B) and the rotational correlation time (τC) . The relevance of this formalism to solid-liquid systems is also demonstrated.