All experimental data of the viscosity (71, the second virial coefficient ( 6 ) and the self-diffusion (pD) (103 experimental points altogether) are approximated in the frame of their experimental ermm by means of an effective isotropic ("4) potential with temperaturedependent p m e t e r s . The UF6 gas at given temperature ( T ) is considered as one vibrationally excited state with a sire avenged over all excitations. The equilibrium distance (r,) increases with temperature according to the vibrational excitation of the molecule. The potential depth w'ell ( E ) decreases with enlargement of the equilibrium distance in order to keep the long range forces unchanged.Pxameters of the ground state-ground state interactions (T = 0 K) are derived by means of a minimiwtion of the sum of the squared deviations between experimental and calculated pmpertres normalized to the expenmental error. Appmxm" formulae for the temperature dependences rhff(T). B ( T ) , q ( T ) and p D ( T ) lo be used for accurate and easy calculations are given. A comparison with available (n-6) potentials is made.defining E and r, is described as finding a cross point of calculated B , q, pD and thermal conductivity as a function of E and r,. Nowadays such a procedure may be considered as too simplified, but it produces a good fit of measured 7 and B for mixtures w6-MoF6 and uF6-w&,, where the parameters of the potentia] are calculated as

The total vibrationally inelastic and the momentum-transfer elastic e-CF3OCF 3 cross sections are obtained by the best fit of the measured electron drift velocity in pure CF3OCF~ as well as in its mixtures with Ar.

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The transport and equilibrium properties of SiF 4 and SiCl 4 are calculated in the temperature range 200-840 K from temperature-dependent, spherically symmetric intermolecular potentials. The potential parameters are obtained by minimization of the deviations between calculated and measured second virial coefficient and viscosity data. The obtained potential parameters are compared with those of the previously studied CF 4 , SiF 4 and CCl 4 .

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The parameters of the temperature-dependent isotropic potentials of binary - and - interactions are obtained from the experimentally measured second virial coefficient B and viscosity of these gases. The parameters of the ground state (equilibrium distance and the potential depth well at , together with the repulsive parameter n and the temperature dependence ) are defined and can be used to calculate any potential-dependent property of the two gases. The measured viscosities of the - and - mixtures at T = 354 K are reproduced within the experimental error using earlier defined potential parameters for .

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