Transport and relaxation of naphthalene in supercritical fluids

The pressure dependence of diffusion coefficients of naphthalene in supercritical CO{sub 2} and naphthalene-d{sub 8} in supercritical ethylene has been measured by using the NMR fixed field gradient spin-echo Bessel function analysis technique. The pressure dependence of the reorientational motion of naphthalene-d{sub 8} in CO{sub 2} and ethylene has been studied by measuring the deuteron spin-lattice relaxation time, T{sub 1}, as a function of pressure at several isotherms. The temperatures were chosen to cover two regions of the naphthalene-supercritical solvent phase diagram. The experimental data allowed the molecular level test of the applicability of the Stokes-Einstein and Debye equations in the binary systems studied. The expression D({eta}/T){sup 0.75} = constant represents the experimental diffusion data well, and the modified Debye equation describes the reorientational motion of naphthalene in supercritical CO{sub 2} and ethylene solvents.