Scattering of particles from a solid surface: the impulsive model of composite encounters

We propose a general impulsive model for scattering of molecules from a flat solid surface. It is assumed within the framework of this model that an encounter of an atom (or ion) with the surface is a series of elastic (in the direction normal to the surface) hits of the atom against surface pseudoparticles, the hits instantly following each other. To each atom, one assigns two infinite sequences of masses of pseudoparticles. The model is a far-reaching generalization of the well-known hard cube model. Criteria for both finiteness and infinity of series of hits are formulated, based on the masses of pseudoparticles and the mass of the atom. It is shown that in virtually all the cases, any number of hits in a series occurs with a positive probability. The proposed model does not satisfy the reciprocity condition.