Photoemission and Electron Detachment in Low-Energy Collisions of Metastable Atoms with Negative Ions

Cross sections for Penning detachment, $X^{*}+Y^{-}\to X+Y+e$, and collision-induced photon emission, $X^{*}+Y^{-}\to X+Y^{-}+h\nu$ have been calculated for collisions of metastable neutral atoms and negative ions at low energies ($E\sim 1$ eV). A semiclassical treatment based on the impact parameter method and adiabatic electronic interactions was employed. Collisions involving ${\mathrm{H}}^{*}$ ($2{}_{}{}^1{}_{}{}^{}S$), ${\mathrm{Ca}}^{*}$ ($3{}_{}{}^1{}_{}{}^{}D$), and ${\mathrm{He}}^{*}$ ($2{}_{}{}^1{}_{}{}^{}S$) with ${\mathrm{H}}^{-}$, ${\mathrm{O}}^{-}$, ${\mathrm{Cl}}^{-}$, and ${\mathrm{C}}^{-}$ were investigated. In all collisions not involving ${\mathrm{H}}^{*}$ ($2{}_{}{}^1{}_{}{}^{}S$), Penning detachment predominates and exhibits cross sections on the order of ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$.