Classical stochastic diffusion theory for thermal desorption from solid surfaces

As a first step in the microscopic study of dynamic processes on surfaces and at interfaces, we have considered the thermal desorption of adsorbed species on solid surfaces. We review recent developments based on a classical stochastic diffusion formulation. Using this theory, we obtained a simple rate expression, R=(Omega0/2pi) f(T)exp(–De/kT), where Omega0 is the surface-adsorbate vibrational frequency and De the dissociation energy. For atoms f(T)=1, whereas for molecules f(T) depends on the parameters for the frustrated rotations at the surface. The effect of coverage on the rate of desorption and the process of desorption into a fluid are also examined. Finally, we discuss the relationship between our theory and the expressions obtained from activated complex (transition-state) theory.