Measurements of the polarization of radiation emitted by fast argon ions scattered by adsorbates on surfaces

The circular polarization of radiation emitted by fast Ar ions in the 4p' ²F _{7}/{2} state was measured following near-grazing collisions with a surface. Under uhv conditions, at 60 keV incident ion energy, the relative Stokes parameter {S}/{I} = 0.38, but with N ₂ and H ₂ gases present and adsorbed on the surface, {S}/{I} = 0.25 and 0.30, respectively. The original polarization was recovered following removal of the gases. These gas-specific, reversible polarization changes are interpreted in terms of formation and orientation of the fast ion state by a final collision involving electron capture from the adsorbates.