Doubly charged negative ions of carbon-60

Abstract

We report the observation of long-lived (\ensuremath{\tau}>${10}^{\mathrm{\ensuremath{-}}3}$ sec) doubly charged negative ions of ${\mathrm{C}}_{60}$ in the gas phase. ${\mathrm{C}}_{60}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{C}}_{60}^{2\mathrm{\ensuremath{-}}}$ ions are produced by laser desorption from a surface covered with ${\mathrm{C}}_{60}$ molecules and are believed to be produced by negative surface ionization from the laser-heated surface. Pseudopotential calculations indicate that ${\mathrm{C}}_{60}^{2\mathrm{\ensuremath{-}}}$ is slightly bound (electron affinity of ${\mathrm{C}}_{60}^{\mathrm{\ensuremath{-}}}$\ensuremath{\simeq}0.1--0.4 eV) relative to ${\mathrm{C}}_{60}^{\mathrm{\ensuremath{-}}}$.