Neutralization of fast alkali-ions after grazing scattering from Al(111) and Ni(111)

We have studied the neutralization of fast Na+- and K+-ions after the interaction with clean and flat Al(111)- and Ni(111)-surfaces at grazing incidence Φ < 1°. The neutral fractions of specularly reflected projectiles show two different classes of dependences on projectile velocity which can be referred to the difference between work function of the target and binding energy of the atomic ground term. Model calculations in the framework of resonance tunneling between metal surface and atom which incorporate the parallel velocity of the projectile by Galilean-transformation and the electronic spin degree of freedom reproduce our experimental data fairly well.