The effects of lattice recoil in photon- or electron-stimulated desorption from metal surfaces are investigated via classical trajectory calculations. Desorption of F atoms from Al(111) surfaces is studied as a model system. The basis for site specificity in desorption is examined by considering different binding sites on flat (111) terraces, and sites at the edges of single atomic steps. We find that the energy transfer to the lattice can be approximated by regarding the metal as an effective mass, with a value which depends on the site, but not on the details of the particle-surface interaction. Lattice recoil also results in a transient change in the local metal charge density, which can affect the desorption probability. © 1989 The American Physical Society.