Kinetic Approach to Condensation

A kinetic formalism including a Boltzmann-like equation is introduced to study classical condensation phenomena in gases. Force laws which include a repulsive core together with an $r^{-N}$ attractive tail are examined for all integral $N$ greater than unity. The theory considers perturbations whose wavelengths are large compared to the diameter of the core. The results fall into two categories depending on whether $N\le 3$ or $N\ge 4$, respectively. For the first class of long-range forces, there are no stable thermodynamic states. For the second class of short-range forces, phase-equilibrium curves are found which are in accord, qualitatively, with classical results. In the limit as $N\to \infty$, all states are stable. A discussion of the effects of random collisions is included.