Isomer-specific trends with charge state in gas-phase reactions of fullerene cations, C-60(x+) (x=1-3), with nitromethane and methyl nitrite: Polymethoxylation of C-60 dications

Rate coefficients and product distributions have been measured for the gas-phase reactions of C-60(.+), C-60(2+) and C-60(. 3+) With nitromethane and methyl nitrite which show a strong dependence of reactivity on the charge state of the fullerene cation and on the nature of the neutral reactant isomer. Furthermore, sequential bimolecular methoxyradical transfer reactions were observed with methyl nitrite leading to the polymethoxylation of C-60(2+) with up to 12 methoxy groups, far more than the number of charges on the C-60 surface. Unusual periodicities were seen in the reaction kinetics, and these are correlated with the radical and aromatic character of the derivatized C-60(OCH3)(n)(2+) cations. The measurements were performed in helium buffer gas at 0.35 +/- 0.01 Torr and 294 +/- 3 K with use of the Selected-Ion Flow Tube (SIFT) technique. Multicollision induced dissociation experiments with the derivatized C-60(OCH3)(n)(2+) (n = 1-4) cations indicated sequential loss of single methoxy radicals, which is consistent with direct bonding of the methoxy, groups to the C-60 cage. Polymethoxylation was not observed with C-60(. 3+). Instead, C-60(. 3+) reacts with methyl nitrite by dissociative electron transfer. C-60(2+) is unreactive with nitromethane, but C-60(. 3+) adds one molecule and the C-60(CH3NO2)(. 3+) adduct ion reacts further only by proton transfer. C-60(.+) is unreactive with both nitromethane and methyl nitrite.