Self-diffusion coefficients D for CH4, C2H6, and C3H8 have been measured at pressures up to 200 MPa and 450 K by the spin echo technique with pulsed field gradients. The experimental results for propane agree with data obtained by recent M. D. simulations with a three-site Lennard-Jones-skeleton model. In the p,T range studied, the experimental self-diffusion coefficients can be described quantitatively by the interacting sphere model and the rough hard sphere model. This implies, that even a single Lennard-Jones potential and diameter can represent the dynamic data for propane quantitatively.

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The pressure dependence of the self diffusion coefficient D for octamethylcyclotetrasiloxane and hexamethylcyclotrisilazane has been determined by the NMR spin echo technique with pulsed magnetic field gradients at pressures up to 200 MPa and at temperatures between 490 K and 290 K. The data extend partially into the deeply supercooled range. The isobaric temperature dependence of these data is quantitatively described by the empirical Vogel-Fulcher-Tammann equation. For both substances the melting pressure curves were determined in addition.