EXPERIMENTAL-STUDY OF REACTIONS OF THE BUCKMINSTERFULLERENE CATIONS C-60(.+), C-60(2+), AND C-60(.3+) WITH AMMONIA AND AMINES IN THE GAS-PHASE

Results of SIFT experiments are reported for ion-molecule reactions initiated by C60.+, C60(2+), and C60(.3+) in ammonia, methylamine, ethylamine, dimethylamine, and trimethylamine at 294 +/- 2 K in helium gas at a pressure of 0.35 +/- 0.02 Torr. The main features of the observed reactions can be described in terms of adduct formation and charge transfer and are in line with the known electron recombination energies of these three fullerene cations. Higher order reactions of the adduct ions display both further adduct formation and proton transfer. Addition is the only primary product channel observed with C60.+. The apparent bimolecular rate coefficient for adduct formation increases systematically from a low value of less than 1 X 10(-12) cm3 molecule-1 s-1 (with NH3) to a value which appears to saturate at about 1 x 10(-9) cm3 molecule-1 s-1, the collision rate coefficient, with decreasing ionization energy of the added amine. C-N bond formation is proposed for these addition reactions and a model is presented which accounts for the trend in the rate coefficients. Secondary adducts were observed to form rapidly with ammonia and all of the amines except trimethylamine and are attributed to the formation of a proton bond. Charge transfer was observed to compete with addition in the reactions of the C60(2+) dication with the amines (NH3 reacted exclusively by addition), increasing in relative importance with decreasing ionization energy of the amine. Secondary adduct formation, although observed with ammonia, methylamine, and ethylamine, was seen to occur in competition with a dominant proton-transfer channel. Addition of up to three molecules of ammonia was observed with C60(.3+), with each adduct also undergoing proton transfer in a secondary reaction with ammonia. The amines react with C60(.3+) exclusively by charge transfer which in the case of ethylamine is largely dissociative. It is proposed that the reactions of C60.+ and C60(2+) provide pathways for nitrogen derivatization of neutral fullerenes in the presence of ionization sources and mechanisms for ion neutralization, as, for example, in interstellar clouds and circumstellar envelopes.