Pair potential monatomic fluids

Comparison with Experiment. We consider systems involving the polar constituents HCl and HBr, and the quadrupolar constituents CO2, ethane, ethylene and acetylene, together with the nonpolar monatomic fluid xenon. For the like pair interaction the Intermolecular potential models used were ... 

As ve stated earlier, it is possible to express all the thermodynamic properties of a liquid in terms of g(r), if we assume that the intermolecular potential is pair-wise additive. The thermodynamic energy is easily expressed in terms of g(r). e shall do this first by a physical argument and then by a formal approach. For a monatomic fluid, the total energy is given by... 

As stressed earlier, the actual pair interaction potential v(r) in a monatomic fluid depends on the quantum nature of the particles and is a function of their distance. No dependence on the temperature in these functions is included. As a matter of principle, such a thing cannot be. This absence is displayed clearly within the exact PI scheme when formulating the quantum statistical problem (e.g., Eqs. 25-27). However, in the semiclassical cases one finds potentials that are built by using the underlying v(r) as a reference, which is corrected so as to include quantum diffraction information (J, h,m) relevant to the system under study. This extra dependence can influence the calculation of semiclassical properties, as indicated by the thermodynamic derivative procedures [120]. 

Precise intermolecular potentials are available for monatomic He, Ne, Ar and Xe. This permits accurate calculations of the VPIE s of these gases, their mixtures, and rare gas isotopomer mixtures. To begin, we are reminded that the mean intermolecular potential energy, , and mean force constant < V2U> can be obtained from the pair correlation function of the fluid, g(r),... 

Fluid microstructure may be characterized in terms of molecular distribution functions. The local number of molecules of type a at a distance between r and r-l-dr from a molecule of type P is Pa T 9afi(r)dr where Pa/j(r) is the spatial pair correlation function. In principle, flr (r) may be determined experimentally by scattering experiments however, results to date are limited to either pure fluids of small molecules or binary mixtures of monatomic species, and no mixture studies have been conducted near a CP. The molecular distribution functions may also be obtained, for molecules interacting by idealized potentials, from molecular simulations and from integral equation theories. 

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