Charge exchange in gas-surface collisions: The three electronic state system

A theoretical treatment of near-resonant charge exchange occurring in gas-surface collisions is presented for a coupled three electronic state system. The surface is represented by a cluster of five metal atoms and the diatomics in molecules procedure is used to construct the gas-surface interaction potentials and nonadiabatic couplings. These are used in the common eikonal formalism which gives a time-dependent description for the evolution of the transition amplitudes and the nuclear positions and momenta. An application is made to a hyperthermal energy sodium atom scattering off a tungsten (110) surface. Results of the ionization probability vs. the initial kinetic energy of the sodium atom are presented. The three electronic channels correspond to a neutral (the initial state) and two ionic channels. In comparison to the two state results, it is found that the extra ionic channel gives rise to additional interference effects but it does not substantially increase the ionization probability.