Landau-Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF（001） surface

There is no available theoretical description of electron transfer from negative projectiles at a velocity below 0.1 a.u.during grazing scattering on insulating surfaces.In this low-velocity range,electron-capture and electron-loss processes coexist.For electron capture,the Demkov model has been successfully used to explain the velocity dependence of the negative-ion fraction formed from fast atoms during grazing scattering on insulating surfaces.For electron loss,we consider that an electron may be transferred from the formed ionic diabatic quasi-molecular state to the formed covalent diabatic quasi-molecular state by the crossing of the potential curves of negative projectiles approaching the surface cations,which can be described by the Landau-Zener two-energy-level crossing model.Combining these two models,we obtain good agreement between the experimental and calculated data for the F-LiF（OOl） collision system,which is briefly discussed.