Self-diffusion in liquid ammonia and deuteroammonia

Coefficients of self‐diffusion have been measured by the spin‐echo technique for neat NH₃ and ND₃ from 200 to 298°K. The data are well represented by ${\text{D=(4.5± 0.2)× 10}}^{\text{−3}}\exp \text{[−(2.07± 0.02)/}\mathrm{RT}]$ for NH₃ and by ${\text{D=(6.0± 0.3)× 10}}^{\text{−3}}\exp \text{[−(2.31± 0.02)/}\mathrm{RT}]$ for ND₃. The difference in activation energy for self‐diffusion between NH₃ and ND₃ is shown to be consistent with the viscosity measurements of Hutchison and O'Reilly. These results are interpreted by means of a quasilattice model for self‐diffusion in the liquid state. Values of the work required to create a molecular vacancy are evaluated from liquid density, isothermal compressibility and the scaled particle theory. The quasilattice model yields pre‐exponential factors for self‐diffusion that are in reasonable agreement with experiment.