Kinetics and Dynamics of Gas-Surface Interaction: The Principles of Detailed Balance and Unitarity

Abstract

Some results of a quantum theory for inelastic scattering, sticking and desorption of gas molecules at surfaces are reviewed. The theory is valid if the time scale τ_life=1/r introduced by the relaxation rates r of the vibrational states of adsorbates is large compared to their vibrational periods Tvib. For sufficiently large activation energies of the adsorbates another time constant Tres, the residence time of adsorbates can be determined from the theory. One then can distinguish essentially three different regimes corresponding to the three time scales τ_vib, τ_life and τ_res. There are two steps leading from one regime to the next one: The solution of the Schrodinger equation leading to the relaxation rates r of the kinetic equation, and the solution of the kinetic equation leading to sticking coefficients, accommodation coefficients, desorption rates and angular and energy distributions of desorbing particles. In all cases the principles of detailed balance and unitarity are very helpful in reducing the number, of independent parameters of the theory and as a check of the results of calculations and experiments.