Charge-transfer reactions in atom scattering from ionic surfaces: A time-dependent wavepacket approach

A diabatic description of charge transfer between atoms and ionic surfaces is presented, specifically examining the F/LiF(100) and F/KI(100) systems f or which experiment shows ion formation to be very efficient. Potential ene rgy surfaces describing the energetics for these systems have been generate d with a semi-empirical scheme. At the site of charge exchange, there is a curve-crossing between the ground state and the state representing charge c apture by the projectile. Quantum dynamics calculations with time-dependent wavepacket methods give an initial ion-formation probability of unity for all cases considered. At lowest energies, the ions cannot escape the surfac e, giving an effective threshold for negative-ion production very close to that observed in experiment. Re-neutralization by charge transfer back to t he conduction band of the solid is also examined.