The principle aims of this thesis include the development ofmodels of sublimation and melting from first principles and the applicationof these models to the rare gases.
A simple physical model is constructed to represent the sublimationof monatomic elements. According to this model, the solidand gas phases are two states of a single physical system. The natureof the phase transition is clearly revealed, and the relations betweenthe vapor pressure, the latent heat, and the transition temperatureare derived. The resulting theory is applied to argon, krypton, andxenon, and good agreement with experiment is found.
For the melting transition, the solid is represented by an anharmonicmodel and the liquid is described by the Percus-Yevick approximation.The behavior of the liquid at high densities is studiedon the isotherms kT/∈ = 1.3, 1.8, and 2.0, where k isBoltzmann's constant, T is the temperature, and e is the well depthof the Lennard-Jones 12-6 pair potential. No solutions of the PercusYevickequation were found for ρσ3 above 1.3, where ρ is theparticle density and σ is the radial parameter of the Lennard-Jonespotential. The liquid structure is found to be very different from thesolid structure near the melting line. The liquid pressures are about50 percent low for experimental melting densities of argon. Thisdiscrepancy gives rise to melting pressures up to twice the experimentalvalues.
