Transport Properties of Liquids, I. 539 a) Diffusion with slow kinetic coupling. This approximation leads to very simple modes according to the solutions (33)This result could also be obtained from the slow exchange limit of the general three component independent fluctuation, Eq. b) Fast exchange limit. Neglecting the higher order contribu-(1 1 ) . tions in q we get: s, = -92 k 3 D N H + 2 k 1 2 c p D 3 k3 + 2k,,cp (34) S-= -(k3 + 2 k 1 2~: ) .The first solution s_ is the kinetic relaxation mode given in (24) and the second one, s+, is identical to the kinetic diffusional mode given in (17) for the three component system.The result confirms the unexpected asymptotic behaviour for low pair fractions, Eq. (21),which is a characteristic of the mutual diffusion process involving a gradient of chemical composition. It is different from Eq. (20) which is obtained in the case of the self-diffusion mechanism with a contribution of fast pair-formation exchange reaction.References T. A. Renner and P. A. Lyons, J. Phys. Chem. 78, 1667 (1974). H.4. Gores, J. Barthel, and P. Turq, to be published.
Selbstdiffusion / Fliissigkeiten / Freies Volumen / Transporterscheinungen / ViskositiitSelf-diffusion coefficient D, viscosity q and density p of nearly spherical molecules (Tetraalkyl-, Tetraalkoxy compounds) and of nearly disk like molecules (crown ethers) were measured (250 5 T/K 5 370). -'H-NMR spin-echo spectroscopy was applied for the measurements of D. q was determined via a Ubbelohde micro-viscosimeter and p via a vibrating densimeter. -D and q follow the Stokes-Einstein-Gierer-Wirtz relation. The free-volume theory of Cohen and Turnbull (CT) was applied to describe the experimental data quantitatively. By introducing geometrical relations for the mean free path I and the critical free volume u; the CT-model was extended and applied to the experimental results. Thereby a very satisfactory description of the measurements is attained. D of the substances investigated can be calculated as function of the melting point and p ( T ) .Empirically the temperature dependence of D ( T ) follow an Arrhenius law. Application of the hybrid equation of Macedo and Litovitz to the experimental data shows that the temperature dependence of the transport properties in van-der-Waals liquids composed of spherical or disk like molecules is mainly determined by the creation of the free volume with increasing temperature. The Raman scattering profiles of the OH stretching vibrations of methanol, ethanol, and n-propanol in the gas phase and of ethanol in alkane solution are measured and analyzed with regard to the conformational behaviour of the molecules. -The fine structure of the profiles is largely resolved because rotational motions do not appreciably contribute to the band width as the scattering tensor is almost isotropic. In the case of ethanol, the assignment of the two sub-bands to the trans and gauche conformers follows from the intensity ratio. An assignment to the five possible conformers is proposed for the complex profile structure...
