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The repulsive wall of the Ar–Ar interaction is reexamined with the purpose of rationalizing the apparent inconsistency between high energy beam results and high temperature transport data. A new piece-wise experimental potential is proposed which predicts not only the beam results but a large set of transport data up to 7000 K. Lower temperature/energy data are predicted almost equally as well as other state-of-the-art empirical potentials. [ABSTRACT FROM AUTHOR]

Recent literature potentials for Ne–Kr and Ne–Xe systems are analyzed and critically assessed as to their abilities to predict dilute gas bulk and microscopic properties. Two new potentials are proposed for the Ne–Kr and Ne–Xe interactions which accurately predict a large number of properties and appear to be the best characterizations of these interactions. [ABSTRACT FROM AUTHOR]

Values of the second refractivity virial coefficients BR of the atomic gases He, Ne, Ar, Kr, and Xe have been measured with a recently improved differential-interferometric technique to a high degree of accuracy. This device basically consists of two coupled grating interferometers. One interferometer, with two similar cells in series, measures differentially the higher-order effects of density while the second interferometer, with two similar cells in parallel, simultaneously measures the absolute value of the refractive index. In the range of pressure investigated (up to 40 MPa), the third refractivity virial coefficient CR becomes significant for the gases Ar, Kr, and Xe and the fourth refractivity virial coefficient DR becomes significant for Xe. The agreement between our experimental BR and the theoretical prediction based on the classical dipole–induced-dipole model is fairly good for Ar, Kr, and Xe but poor for He and Ne. For He and Ne, however, good agreement is obtained when a semiclassical approach is used. Accurate values of the first refractivity virial coefficients AR were determined independently by making absolute measurements of the refractive index as a function of pressure. [ABSTRACT FROM AUTHOR]

In order to address the problem of three-body interactions in gas–surface scattering, we considered the collision of a He atom with the (0001) surface of graphite coated by a monolayer of Xe. To eliminate the uncertainties connected with errors in the two-body He–Xe interaction, we determined the latter by crossed-beam differential collision cross-section measurements performed at two energies (67.2 and 22.35 meV). These scattering data together with room-temperature bulk diffusion data are then fitted with a Hartree–Fock–dispersion–type function to yield an interaction potential that explains most of the properties of this system within the experimental errors and represents an improvement on previously published He–Xe potentials. Helium diffraction measurements are then carried out from the Xe overlayer and the dependence of the specular intensity from the angle of incidence is carefully determined. Further, a He–surface potential is constructed by adding together the following terms: (1) the He–Xe pairwise sum, (2) the long-range He–(0001)C interaction, (3) the three-body contribution generated by the Axilrod–Teller–Muto term, (4) the so-called surface-mediated three-body interaction He–Xe–(0001)C first considered by A. D. McLachlan [Mol. Phys. 7, 381 (1964)], and finally (5) a small correction which is meant to take into account the nonstationary nature of the surface. Using this potential, well-converged close-coupling scattering calculations are carried out, and their results compared with the data. In general, good agreement is obtained. The agreement can, however, be improved by (a) an increase of about 30% in the contribution of three-body forces, (b) the lowering of the He–graphite long-range attraction coefficient by about 15%, or (c) a reduction of the two-body interaction well depth of 1.6% (the experimental error) together with any combination of the... [ABSTRACT FROM AUTHOR]