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

Abstract

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(001) collision system, which is briefly discussed.

Evidence for the Formation of a Local Pre-Existing Surface Band-Gap Electronic State by F– Projectile Grazing Scattering from a LiF(001) Surface

“…The inexistence of single or double holes necessary for the formation of a single neutral exciton or a trion on a clean and flat LiF(001) surface leads to the destruction of large F – ions due to the inability to form neutral surface excitons , or trions . For a F – projectile collision with a lattice Li + ion at a LiF(001) surface, the electron loss to this Li + ion by forming a quasi-molecular nonadiabatic potential energy curve crossing, requiring a small crossing distance of R c = 1.6 a.u., hardly occurred for the present projectile energy range ( E p ≤ 4.374 keV) and incident geometry (α = 1°). However, experimental results show that for F – projectile grazing scattering from a LiF(001) surface within a velocity range of v < 0.1 a.u., there is a large loss of incident negative ions in the reflected beam (see the black solid circles in Figure a), for which no explanation has thus far been given.…”

Geometrical representation of coherent tunneling process in two-waveguide and three-waveguide coupler

“…Landau-Zener (LZ) non-adiabatic tunneling process and stimulated Raman adiabatic passage (STIRAP) have different physical mechanisms and have aroused wide interest during the past two decades. For instance, the former has been widely used in waveguide arrays, [1,2] electron transfer on insulating surface, [3] Bose-Einstein condensate, [4,5] Bose-Fermi mixture, [6] optical lattices, [7] radio frequency superconducting quantum interference, [8] preparation of quantum state, [9] coherent destruction of tunneling, [10] to name a few, while the latter has been used in waveguide optics, [11][12][13] population transfer in atomic and molecular physics, [14][15][16][17][18] Bose-Einstein condensate, [19,20] generation of terahertz pulses, [21] optical storage, [22] and so forth. Shore et al have discussed the differences between the STIRAP in three-level atom system and LZ tunneling process in four-state model.…”