Self-diffusion in gaseous and liquid ethylene

Proton spin echoes at 24 MHz have been used in an accurate study of the self-diffusion coefficient in gaseous and liquid ethylene over a large range of density and temperature. The high temperature data are well described by the corrected Enskog theory. As the temperature is lowered, increasing deviations from the hard sphere behaviour are observed, which are in qualitative agreement with computer simulations on square-well and Lennard-Jones particles.