The fundamental processes of SiCl2 desorption from Si(1 1 1) surfaces are investigated, by using the first-principles pseudopotential method in a local density approximation. It is shown that the surface diffusion of Cl and SiCl Units have a small activation barrier around 0.9 eV. while the Formation and the evaporation of SiCl, have a large activation energy around 2.1 eV. The rate equations based on these energies Clarify that the desorption is a second order process of chloride coverage made up of two successive reactions. (C) 2002 Elsevier Science B.V. All rights reserved.