Interaction of Gas Atom with a Hot Solid Surface: A Harmonic Model Analysis

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Abstract
The interaction of a monoenergetic gas beam with a hot surface is viewed as a collection of discrete two-body collisions. By use of a soft-cube model with a truncated harmonic interaction potential, the interaction is reduced to a linear problem. The solution to this simplified view indicates that an important role of thermal motion of the solid atoms is reflected in the distribution of their initial conditions at the time interaction begins. Specifically, the initial condition distribution is biased toward interactions beginning with greater than average relative velocity between gas and solid atoms. The average exit velocity of the gas is expressed as an integral over the initial condition distributions. This integral cannot be evaluated exactly in closed form and an approximate analytical evaluation is obtained. A computer simulation of the problem was devised and shows satisfactory agreement with the theoretical value for the average relative velocity at the start of interaction and the analytical approximation for the average gas exit velocity.