REPEATED ADDITION OF ATOMIC-HYDROGEN TO FULLERENE CATIONS, DICATIONS AND TRICATIONS

The reactivity of the fullerene cations C-56(n+), C-58(n+), and C-60(n +) (n = 1, 2, 3) with atomic hydrogen has been studied in a selected-i on flow tube apparatus at a temperature of 294 +/- 2 K and a helium bu ffer-gas pressure of 0.36 +/- 0.01 Torr. Repeated addition of hydrogen atoms was inferred in the reactions of all the fullerene cations. Rat e coefficients for each hydrogen-atom addition step could not be deter mined separately. However, a ''mean addition rate coefficient'' for th e observed series of sequential hydrogen-atom additions could be deter mined, yielding values of 3.0 x 10(-10)-4.5 x 10(-10) cm(3) molecule(- 1) s(-1) for singly and doubly charged fullerene ions, and 8.0 x 10(-1 0)-10 x 10(-10) cm(3) molecule(-1) s(-1) for fullerene trications. The lower limits obtained for the effective bimolecular rate coefficient for the primary addition step were 1.0 x 10(-10) cm(3) molecule(-1) s( -1), 3.0 x 10(-10) cm(3) molecule(-1) s(-1), and 1.0 x 10(-9) cm(3) mo lecule(-1) s(-1) for singly, doubly and triply charged cations, respec tively. In contrast with previous studies which have established a sub stantial enhancement in the efficiency of addition to the adjacent-pen tagon fullerene ions C-56(n+) and C-58(n+) over addition to the isolat ed-pentagon fullerene ions C-60(n+), little or no difference in the ra te of addition or the overall extent of hydrogenation was apparent bet ween C-56(n+), C-58(n+), and C-60(n+) ions possessing the same degree of positive charge. None of the fullerene cations reacted measurably w ith H-2 under the experimental conditions.