T,p-Dependence of the self-diffusion and spin–lattice relaxation in fluid hydrogen and deuterium

Abstract

Self-diffusion coefficients D were studied for fluid hydrogen and fluid deuterium at pressures up to 200 MPa and in the temperature range 171–372 K by the spin echo method. Spin–lattice relaxation times of both nuclei were measured in the same p,T range. The diffusion coefficients D are described by the rough hard sphere (RHS) model invoking the rotation translation coupling parameter A = 1. Activation parameters are also derived. The dynamic isotope effect of D given by D_r = D(H₂)/D(D₂) is a function of p and T and varies from D_r≈1.1 at the lowest pressures and highest temperatures to D_r≈1.3 for the highest pressures and lowest temperatures reached. The spin–lattice relaxation is for both compounds dominated by the spin–rotation interaction. Only for T₁(H₂) at T = 171 K can a minor contribution from dipole–dipole relaxation be derived from the data.