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Os 3 (CO) 10 (NCCH 3 ) 2 has been hydrogenated with para-hydrogen to yield H 2 Os 3 (CO) 10 where the two hydrogen nuclei remain magnetically equivalent and therefore in a singlet state. Despite this equivalence, an enhanced longitudinal magnetization is observed to decrease toward thermal equilibrium. It is postulated that this enhanced magnetization is created through a nuclear relaxation interference mechanism (cross-correlation between dipolar interaction and chemical shift anisotropy); decay curves are then successfully analyzed by means of a spin relaxation theory adapted to this situation.

Decylammonium chloride dissolved in water at concentrations of 0.5 and 2.0 M has been studied by multifield carbon-13 and deuterium nuclear magnetic relaxation. Carbon-13 longitudinal relaxation times , and nuclear Overhauser effects have been obtained for all carbons in the aliphatic chain, at frequencies ranging from 15 to 90 MHz. Decylammonium chloride has been selectively deuterated at the a position with respect to the polar head. 2H longitudinal relaxation times T[ and, in some instances, transverse relaxation times T2 have been measured from 2 to 55 MHz. At 0.5 M decylammonium chloride forms spherical micelles. The relevant data are consistently analyzed according to the "two-step model" (Halle, B.; Wennerstrom, H. J. Chem. Phys. 1981, 75, 1928, which implies correlation times associated with the local fast motions, ß (/ = 1, 10), a correlation time associated with the slow overall motion of surfactant molecules, rs, and local order parameters S¡. The 2.0 M solution data required a more elaborate analysis (three-step model), which involves two correlation times (corresponding to rotation about the different axes of an ellipsoid) for describing the slow motions. This is because, at this concentration, micelles have nonspherical shape. In both cases, slow correlation times could be interpreted in terms of micelle tumbling and lateral diffusion of surfactant molecules around the curved surface of the aggregate. Quantitative parameters could be deduced. The radius of spherical micelles is identical with the surfactant extended chain length. At 2 M concentration, micelles are rod-shaped. When approximated by an ellipsoid, it is shown that the minor axis is identical with the radius of spherical micelles whereas the major axis is 9 times as large as the latter. The lateral diffusion coefficient is found to be the same in the two types of micelles D = (1.5 ± 0.2) X 10"10 m2 s"1. The fast correlation times confirm the liquidlike character of the micelle interior and the order parameters exhibit the usual profile starting from 0.2 at the a position to very small values at the terminal methyl.

The self-diffusion coefficients of N(CH 3 ) 4 + ions in a cation-exchange membrane, the Nafion, have been measured at different time scales. The time range extends from the picosecond with neutron quasi-elastic scattering experiments to the second with NMR experiments and tens of seconds with radiotracer experiments. At short times, the values of self-diffusion coefficient in the membrane are equal to those in nonconfined solution; the diffusion process is governed by ion-solvent collisions. The NMR results present two different time scales: for short times (<1 s), the self-diffusion coefficient depends both on time and on electrolyte concentration; for long times, these two dependencies disappear. The radiotracer method confirms the NMR results at long time scales: the diffusion does not depend on electrolyte concentration.