Boundary relaxation of a vibrationally excited gas

The relaxation of a nonequilibrium, vibrationally excited gas, consisting of symmetric diatomic molecules, due to collision with the wall enclosing the gas, is considered. Collisions with the walls remove the vibrational excitation of the molecules. The vibrational energy is distributed among the kinetic degrees of freedom of the molecule and the surface, which can be simulated by a set of harmonic oscillators. An equation is derived for the time variation of the temperature T of the kinetic degrees of freedom of the gas. When T is close to the temperature of the surface and to the population temperature of the vibrational state, this equation reduces to the relaxation type. The characteristic time of boundary relaxation depends on the parameters of the gas and of the surface. It is shown that in a certain range of the parameters, boundary relaxation may be more important than the usual relaxation due to pair collisions.