Fluids with Weak Long-Range Forces

Abstract

We consider a classical system of particles interacting via a pair potential consisting of a strong short-range repulsion us(r) and a weak long-range potential of the form ul(r)=γ3 F(γr), where the range γ−1 is long compared with the range of us. The systematic expansion of the thermodynamic quantities in the ratio of the two ranges has been developed previously and is briefly reviewed. The expansion breaks down when the inverse compressibility of the fluid vanishes. Explicit calculations of the equation of state for special choices of the two parts of the intermolecular potential are presented and compared with the corresponding experimental results for argon. It is also shown that to first order in the expansion parameter the specific heat cv has a maximum near the critical isochore.

Infrared and Raman Investigation of Condensed Phases of Methylamine and Its Deuterium Derivatives

“…However, it is not justified to assign the vibration at 3290 cm-1 solely to "1 and that at 3207 cm-l solely to 2"4, because they too are in Fermi resonance with each other. 12 The unperturbed value of the vibration "1 of the associates lies at a wavenumber yet lower than 3290 cm-l . Therefore, the frequency shift to the vibration of monomers at 3340 cm-l is considerably greater than the shift of the antisymmetric NH2 stretching "10 of the associates at 3365 cm-1 to the vibration of monomers at 3400 cm-l .…”

A liquid-state theory that remains successful in the critical region

“…These positive features became hallmarks of successful thermodynamic perturbation theories for simple fluids and were shared by the versions [2] that followed the Barker and Henderson work as well as an alternative perturbative approach set forth somewhat earlier by Hauge and Hemmer [3] that was based on using the inverse range of the attractive interaction rather than its strength as a perturbation parameter. Integral-equation approaches with improved self-consistency were also developed subsequently to yield accurate liquid-state thermodynamics [4].…”