Summary: Gas-Surface Interaction
If we want to solve the Boltzmann equation, we need to specify
boundary conditions for the velocity distribution function at solid
surfaces. Thus, we need to know how incident molecules
interact with a solid surface.
In other words, we need to have a model of gas-surface
In general, molecules can be adsorbed, move around the surface
or undergo chemical reaction with the surface molecules. We will
treat collisions as instantaneous and local.
Accurate modeling of gas surface interaction is very complicated
due to lack of complete knowledge of surface properties (surface
finish, cleanliness, adsorbed gas layers, etc.) and due to lack of
accurate surface interaction potentials.
Specular reflection is mirror like reflection. Specular
reflection happens for
Smooth metal surface that has been outgassed through
exposure to high vacuum and temperatures (baked