Nuclear spin-lattice relaxation and molecular motion in benzene and some benzene derivatives

Proton spin-lattice relaxation times, T1, have been measured in liquid benzene, liquid 1,3,5 trideuterobenzene and liquid bromobenzene, over a wide temperature range. The T1's of these liquids for a series of solutions in their respective perdeuterated analogues are also reported. The intermolecular and intramolecular contributions to T1 are separated by the technique of extrapolation to zero concentration. An experimental technique for separating the intramolecular dipolar and spin-rotation contributions to T1 is discussed for the cases of benzene and 1,3,5 trideuterobenzene. The results of this separation are examined critically in the light of independent measurements of similar parameters. Reliable values for the reorientational correlation time, τd, are obtained. An attempt to separate out a possible intermolecular spin-rotation interaction is discussed. Approximations for the intramolecular dipolar interaction for a many spin molecule are discussed. A simple indication of departure from non-exponential decay is considered and compared with more rigorous theory.