Ion Orientation by Interaction with Adsorbed Gases on Surfaces

Large reversible changes have been observed in the orientation of the $4p^{\prime }{}_{}{}^2{}_{}{}^{}F_{\frac{7}{2}}^{}{}_{}{}^{}$ level of fast ${\mathrm{Ar}}^{+}$ ions excited by scattering from surfaces with chemisorbed ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{H}}_2$ gases. Equilibrium values of the circular polarization fraction $\frac{S}{I}$ of the decay radiation at 461 nm are related to surface coverage, to the adsorbed species, and to the adsorbant metal. An interpretation in terms of multiple collisions ending with charge transfer is discussed.