Collision Density of Hot Atoms

Abstract

The energy‐dependent collision density of hot atoms is discussed and evaluated for several cases. A model is considered in which hot atoms collide with a single species of thermal atoms at energies where the asymptotic solutions of the Boltzmann equation are valid. Elastic nonreactive collisions between unlike species are treated in detail. It is shown that the assumption made by Wolfgang and other workers that the collision density is given by 1/Eα(E), where α is the mean logarithmic energy decrement of the hot atoms, is generally reasonable, but that error may be introduced if the energy dependence of α is not explicitly taken into account. Results are obtained for a class of interaction potentials which includes the inverse power potential, V = K/r^s. The degree of scattering anisotropy is directly related to the exponent s of this potential: s = ∞ corresponds to isotropic (hard‐sphere) scattering, and s = 1 represents the limiting anisotropic case of pure Coulombic scattering. A quantitative estimate of the influence of anisotropy on the collision density is thus provided by the results obtained. An example is then given to illustrate the application of the techniques shown to systems in which reactions occur.