Dynamics of temporary negative ion formation in He+ ion neutralization at an Al(1 0 0)/K surface

Abstract Spin labelling techniques, specifically the use of electron-spin-polarized He + ions coupled with measurements of the ejected electron polarization, are used to examine the dynamics of transient He −* (1s 2s 2 ) ion formation at an Al(1 0 0) surface with a submonolayer coverage ( Θ =0.15) of potassium. The data show that, contrary to some earlier suggestions, the He −* ions are created by a two-step process in which the incident He + ions are first neutralized by resonant tunneling of an electron from the surface into the 2s orbital. A second electron is then captured into the 2s orbital to form the He −* ion.