Transport and equilibrium properties of UF₆gas simultaneously fitted by an effective isotropic potential with temperature-dependent parameters

Abstract

All experimental data of the viscosity ( eta ), the second virial coefficient (B) and the self-diffusion ( rho D) (103 experimental points altogether) are approximated in the frame of their experimental errors by means of an effective isotropic (n-6) potential with temperature-dependent parameters. The UF6 gas at given temperature (T) is considered as one vibrationally excited state with a size averaged over all excitations. The equilibrium distance (rm) increases with temperature according to the vibrational excitation of the molecule. The potential depth well ( epsilon ) decreases with enlargement of the equilibrium distance in order to keep the long range forces unchanged. Parameters of the ground state-ground state interactions (T=0 K) are derived by means of a minimization of the sum of the squared deviations between experimental and calculated properties normalized to the experimental error. Approximate formulae for the temperature dependences rmeff(T), B(T), eta (T) and rho D(T) to be used for accurate and easy calculations are given. A comparison with available (n-6) potentials is made.