Quasiclassical expression for inelastic energy losses in atomic particle collisions below the Bohr velocity.

Abstract

A quasiclassical formula for inelastic energy losses in collisions of slow ions and atoms has been derived. The electronic stopping power is assumed to be due to a momentum transfer during scattering of the target atom's electrons in the screened Coulomb field of the projectile and vice versa. The Coulomb repulsion between the nuclei of colliding particles is shown to decrease greatly the electronic stopping in the limiting case of small, reduced energies, E\ensuremath{\ll}1. This leads to inelastic energy losses being no longer linearly dependent on the particle velocity, as predicted by the linear-response theory. The latter effect explains the experimentally observed strong dependence of the kinetic electron emission well below the threshold on the energy of ions bombarding a solid surface. At relatively large energies (E>1) the expression obtained reduces to the result found earlier by Lindhard and Scharff [Phys. Rev. 124, 128 (1961)]. The total energy losses of slow atoms calculated on the basis of the formula derived for the inelastic stopping power and the expression for the elastic energy losses available in the literature are in good agreement with the experimental data.