Time-dependent quantum calculations of negative ion formation in scattering of atoms from alkali-halide surfaces

Wavepacket methods have been applied to study the motion of atoms above insulator surfaces. In this approach, no assumptions need be made about the motion, energy is conserved and the correct balance of normal and parallel momenta can be maintained, when a non-adiabatic transfer between potential energy surfaces (PESs) occurs. Ion formation probabilities are shown to be sensitive to the coupling between diabatic PESs, in particular, manipulation of the coupling is required to produce a threshold. Trapping is found to be important in the results at low energies, but this is not seen in experiment. The introduction of screening of the hole left on the surface after charge transfer eliminates the trapping.