Dissociative Attachment in Electron Scattering from CondensedO2and CO

The formation of ${\mathrm{O}}^{-}$ and ${\mathrm{C}}^{-}$ ions via dissociative attachment in electron scattering from ${\mathrm{O}}_2$ and CO condensed on a polycrystalline platinum surface is reported. Below 15-eV impact energy, ${\mathrm{O}}^{-}$ from ${\mathrm{O}}_2$ arises essentially from the repulsive ${}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state of ${\mathrm{O}}_2^{-}$, whereas in CO, ${\mathrm{C}}^{-}$ and ${\mathrm{O}}^{-}$ appear to be emitted from higher-energy repulsive states of C${\mathrm{O}}^{-}$ with yields much different from those found for the isolated molecule.