Hydrogen scattering from a LiF ionic surface: Madelung potential and localenvironment effects

The negative ion formation for large angle hydrogen scattering by a LiF sur face is studied within a time-dependent Hartree-Fock approximation of the A nderson's model Hamiltonian. The effect of the Madelung potential on the pr ojectile energy level shifts is modeled by including the point-charge field of the LiF semicrystal in the calculation of the interaction Hamiltonian p arameters. Comparisons between results obtained by a linear-chain model and a description of the solid target based on a cluster approach, allow to in fer the effects of the local environment on the charge exchange process. It is found that H- formation is enhanced in the hydrogen scattering by the a lkali Li+ ions when the F- nearest neighbors are included. The scattering o f H+ within a spinless picture is also analyzed for both descriptions of th e target. The H-1s energy level variations along the trajectory, and the qu asimolecular states originated by the adiabatic interaction between the pro jectile state and the core states of the target, mainly determine the H+ ne utralization probability and also the electronic excitations in the solid. [S0163-1829(99)03219-1].