The problem of planar condensation/evaporation of a monatomic vapor is solved based on the linearized Boltzmann equation. Accurate numerical results for the pressure and temperature jumps, and the macroscopic profiles for the density and temperature are reported for rigid sphere molecular interaction. Variational expressions for the jumps for several different molecular force laws are evaluated. For rigid spheres, these agree well with the numerical results but are otherwise found to be relatively insensitive to the intermolecular force laws.