The Negative Ion Fraction Dynamic Equilibrium In Grazing Scattering Neutral H Atoms From A LiF(100) Surface

Charged particle–surface interactions have been intensively studied over the past two decades,for understanding various fundamental processes that are important in catalysis,development of gas sensors,problems of adhesion etc.the dynamics of electron transfer plays an important role in chemisorption and reactions at surfaces.These information can be obtained from charge state analysis of scattered particles by atoms or ions grazing scattering off various ionic-crystal surfaces.The process of atoms or ions interacting with a metal target has been explained by the resonant electron capture mechanism.Basically,the image potential shifts the affinity level of the projectile when it approaches or leaves the metal surface.Thus,electrons are transferred between the affinity level of the projectile and the electronic state of the metal when the affinity level is resonant with occupied or unoccupied electronic states of the metal.For atoms or ions interacting with an ionic crystal target,a surprisingly large fraction of negative ion was observed in the experiment.Recent studies have focused on electron emission and energy loss of the projectile and charge transfer phenomena for atoms or ions interacting with an ionic crystal target,because its offers a potential technological application in ion sources and atom detection for space research.In this work,taking into account both key effects—ML polarization and image interactions in electron capture and considering into the Coulomb barrier tunneling of the affinity electron on the formed negative-ion during their interaction with surface anion sites,reproducing the complete velocity range of negative-ion formation in grazing scattering neutral H atoms from a LiF(100)surface.The fraction of negative hydrogen ions is explained by a model of a series of capture and loss cycles for the grazing scattering of neutral H atoms from a Li F(100)surface over the complete velocity range,employing the Demkov model to describe the probability of electron capture and employing the Landau–Zener and Rost models to describe the probabilities of electron transfer to the surface exciton level and ejection into vacuum,respectivelyThe negative hydrogen ion that is formed by neutral H atom capture of an electron from an site of an ionic crystal surface is the common precursor for these electronic processes,which occur along the incoming and outgoing projectile trajectory in a collision.The calculation results are found to be in good agreement with the available experimental measurement,and we found that the final fraction of negative hydrogen ion formation is the dynamic equilibrium value of successive cycles of electron capture and loss,which is independent of collision times and only depend on the distance between projectiles and the ion crystal surface for different electronic processes.The speed threshold for the formation of negative ions is mainly controlled by the electronic process of electron transfer to the surface exciton level.In the process of negative ion formation,the fraction of negative ions is related only to the projectile velocity.