General impulsive models of scattering of molecules from a solid surface without tangential forces

Abstract

We propose a general impulsive model for scattering of a system of atoms or ions from a flat solid surface without tangential forces (that is, forces parallel to the surface). It is assumed within the framework of this model that each individual encounter of an atom with the surface is a series of elastic hits of the atom against surface pseudoparticles, the hits instantly following each other. A distinctive feature of the model is that to each atom, one assigns two infinite sequences of masses of pseudoparticles. Criteria for both finiteness and infinity of series of elastic hits are formulated, based on the masses of the pseudoparticles and the mass of the atom. The model is a far-reaching generalization of the well-known "hard-cube model" for scattering of atoms from a solid surface. We illustrate (by some simplest examples related to scattering of potassium iodide molecules) an application of the correlation analysis to the study of the dependence of the dynamical characteristics of the scattering on the masses of the surface pseudoparticles. The absence of tangential forces seems to be a substantial limitation of the model (for instance, the recent experimental data on scattering of KI from a diamond surface indicate that tangential forces play a significant role in this process).Keywords: scattering of molecules from a surface, impulsive model, surface pseudoparticles, potassium iodide, dissociation, correlation analysis.The dependences of the number of trajectory types on the "vertical component" of the energy of molecules in the beam for the two values of the surface temperature s T and for the two options of the "collisional" and "Maxwellian" masses Физико-химическая кинетика в газовой динамике 2019 Т.20 (1)

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

“…Finally, we set M 1,j = Λ j m C where Λ j is the mean number of carbon atoms in a graphite layer "covered" by a disc of radius R j . The procedure for determining the coefficients Λ j is described in detail in the papers [1,2]. According to Sects.…”

“…. from a solid surface [1,2]. To each atom A j , one assigns its mass m j > 0, its radius R j > 0, a sequence of "collisional" masses {M n,j } n≥1 (0 < M n,j ≤ +∞), a sequence of "Maxwellian" masses {µ n,j } n≥1 (0 < µ n,j ≤ +∞), and a sequence {L n,j } n≥1 of laws of the change in the "horizontal" component of the atom velocity (of course, it is assumed that the choice of these masses and laws is physically motivated).…”

“…In our opinion, the composite encounter model is sufficiently flexible (the law of the change in the atom velocity component normal to the surface includes infinitely many parameters) and possesses a rather interesting mathematical structure. A preliminary version of the model was expounded in Russian in the work [2], while its particular case pertaining to ionic dissociation of potassium iodide molecules at a graphite surface was presented in the paper [1]. A simulation of this dissociation via the composite encounter model within the framework of the quasiclassical trajectory method [1] and the additional calculations of the work [2] have confirmed that the model is very easy to implement for computers.…”

“…A preliminary version of the model was expounded in Russian in the work [2], while its particular case pertaining to ionic dissociation of potassium iodide molecules at a graphite surface was presented in the paper [1]. A simulation of this dissociation via the composite encounter model within the framework of the quasiclassical trajectory method [1] and the additional calculations of the work [2] have confirmed that the model is very easy to implement for computers.…”

“…The Logan-Stickney model is impulsive: the atom-surface interaction in this model is considered as an elastic hit of the atom against a certain pseudoparticle ("cube") which is moving normally to the surface assumed to be flat, while the component of the atom velocity parallel to the surface is conserved. Impulsive models of scattering of atoms or molecules from a surface, developing the hard cube model, have been used in chemical physics until very recently (see, e.g., [1,2,6,11,15,18]). The role of simple models and, in particular, of Logan-Stickney-type models in the contemporary theory of gas-surface interactions is discussed in the survey [9].…”