Classical Stociias’i’ic Diffusion Theory for Desori’tion from Solid Surfaces

We present a theory of desorption of atoms and molecules from solid surfaces based on a chtssical stochastic diffusion formulation. We obtain a simple rate expression which has the form R = (D,/2n) j(T) exp( D,/k,), where T is the temperature, k is Boltxmann’s constant, 0, is the bond enthalpy, and sd, is the surface-adsorbate vibrational frequency. For atoms j(T) = 1, while for molecules j(T) depends on the parameters for the frustrated rotations at the surface. Application of this theory is reported for the desorption of atoms and molecules. We find that molecules lead to a greatly increased (factor of 100) Arrhenius pr~xponential factor in excellent agreement with experiment.