Nuclear Spin-Lattice Relaxation in Solutions

Abstract

T 1 for protons in C6H5Cl, C6H6, and C6H12 has been measured as a function of concentration in solution with CS2 and CCl4. T1 does not have the dependence on the solution viscosity suggested by the theory of Debye. The rotational relaxation times at infinite dilution are obtained by extrapolation, and the correlation times calculated from these results are compared with the values predicted by the rotating sphere model as well as an inner viscosity and microviscosity model. The inner viscosity model provides the best agreement with the experimental results. The correlation times are found not to be proportional to the volumes of the molecules but seem to be simply related to the moments of inertia as well as the masses of the molecules of interest and the masses of the solvent molecules. An approximate formula which provides good results for the systems above is suggested as τ=2Iηa/μkT, where I is the moment of inertia of the molecule of interest, η is the solvent viscosity, a is the average radius of the molecule, and μ is the reduced mass of the solvent-solute system.