Hydrogenation of fullerene cations in the gas phase: reactions of fullerene cations and dications with atomic and molecular hydrogen

Abstract

The recent discovery' and synthesisZ of the fullerene series of carbon allotropes has opened up many exciting vistas in chemistry? So far, hydrogenation of fullerenes has been achieved in solution by the Birch reduction, but only with C60.4 C60H36 was the observed product, and ab initio calculations have predicted that C&, should also be table.^ A previous attempt to hydrogenate the monocation of Cm in the gas phase was unsuccessful-C60*+ has been found to be unreactive toward molecular hydrogen6-but the monohydrogenated Cm and C70 cations have been formed by gas-phase proton t r a n ~ f e r . ~ Here we report results of an experimental study which demonstrate that both the monocations and the dications of Cm and C70 can be hydrogenated in the gas phase by reactions with atomic hydrogen. We have studied the reactions of Cm*+, c60z+, C70*+, and C70z+ with H and with Hz and can report that all of these fullerene ions are observed to add atomic hydrogen with remarkably high efficiency. Hydrogenation of fullerene cations in this manner has importance in the chemistry of sooting flames* and in the chemistry which leads to partially hydrogenated fullerane molecules in interstellar clouds and circumstellar envelope~.~J~ Atomic hydrogen (atomic deuterium) was produced by the action of a microwave discharge upon a dilute mixture, -3%, of Hz (D2) in He. The discharge source and the method of calibrating the dissociation efficiency have been described previously,*'z as has the selected ion flow tube (SIFT) apparatus used in these experiments to measure reaction kinetic^.'^ Fullerene ions were produced by electron bombardment (at 50 eV) of c 6 0 and C70 vapor entrained in argon carrier gas. The fullerene sample