Pressure Dependence of Self-Diffusion in Fluid NH3 and ND3.

Abstract

Self-diffusion coefficients D for fluid NH3 and ND3 have been obtained at high pressures by the NMR pulsed field gradient method for the first time between the melting pressure curve and 473K at pressures up to 200 MPa. The ratio P(113)/T3)]T,p defines the dynamic isotope effect. It has a very small p-dependence and a significant Tdependence. Compared to H2O and the lower alcohols D of ammonia shows a surprisingly weak p and T dependence. The data are analysed in the rough-hard-sphere (RHS) model. The A-parameter of this model gives no indication for the influence of hydrogen bonding upon the translational dynamics in fluid ammonia.