Collision of Li+ and Na+ with C60: Insertion, fragmentation, and thermionic emission

Abstract

Interactions of ${\mathrm{Li}}^{+}$ and ${\mathrm{Na}}^{+}$ with ${\mathrm{C}}_{60}$ molecules have been studied over the collision energy range from 0 to 150 eV. We observe insertion of the alkali-metal ions to form the endohedral [${\mathrm{LiC}}_{60}$ ${]}^{+}$ and [${\mathrm{NaC}}_{60}$ ${]}^{+}$ species, with energy thresholds of 6 and 20 eV, respectively. At higher collision energies, the excited [${\mathrm{NaC}}_{60}$ ${]}^{+}$ appears to relax mainly by loss of ${\mathrm{C}}_2$ units from the fullerene cage, yielding [${\mathrm{NaC}}_{60\mathrm{-}2\mathit{n}}$ ${]}^{+}$. For [${\mathrm{LiC}}_{60}$ ${]}^{+}$, escape of the ${\mathrm{Li}}^{+}$ competes effectively with ${\mathrm{C}}_2$ loss. For both ${\mathrm{Li}}^{+}$ and ${\mathrm{Na}}^{+}$, the signal for pure carbon fragment ions ${\mathrm{C}}_{60\mathrm{-}2\mathit{n}}^{+}$ increases sharply at ∼30 eV, which is attributed to thermionic emission.