Excitations in charge-transfer atom scattering

The electronic excitations are calculated for a tight-binding model of 25–1000 eV Na atoms scattering off W, assuming a classical trajectory for the Na atoms which interact with a single half-filled band on the substrate. The excitation spectrum consists of substrate electron-hole pairs at low energies, with a jump at the ionization threshold due to electron transfer from the Na to the W. If the Na ionization level crosses the Fermi energy beyond the range of hopping between the Na and the W substrate, the ionization probability is high. As the Na kinetic energy is reduced the ionization probability decreases, but the substrate electron-hole excitations increase in importance, and this is discussed in semi-classical terms.