A simple model for the dynamic accommodation coefficient

Landau Institute for Theoretical Physics, RAS - 142432, Chernogolovka, Moscow Region, Russia

Received: 4 February 2020
Accepted: 27 May 2020

Abstract

Collisions of particles (e.g., gas atoms) with a bulk condensed matter body are never pure elastic ones. The kinetic energy of the incident particles partially transfers to the internal degrees of freedom of the bulk body (or inversely, particles can acquire some energy from the condensed matter system excitations). In this paper following the notorious Landau work (Landau L. D., Phys. Z. Sowjetunion, 8 (1935) 489) we propose a simple model to calculate the dynamic accommodation coefficient (which directly relates to the speed of the reflected and incident particles). Our motivation to revisit the 85-year-old Landau work is due to two new results emanating from our consideration: i) we found the dynamic accommodation coefficient for the particles reflected from the crystalline body surface (whereas Landau studied particles reflected from liquids); ii) our results are not based on the perturbation theory (basically used in the Landau paper). Of course there is a price to pay for the generalization of the Landau theory. To make explicit calculations feasible, we need a specific model for the solid body, and its interaction with incident particles. We assume pure harmonic solid crystal dynamics and the same harmonic interaction with the incident particles (while Landau studied the interaction exponentially decaying with the distance from liquid surface). The results can be used as a certain express-analysis guide for much more involved simulation methods.