GAS-PHASE REACTIONS OF FULLERENE MONOCATIONS, DICATIONS, AND TRICATIONS WITH NITRILES

Results are reported for the reactions of the fullerene ions C60.+, C70.+, C60(2+), C70(2+), and C60.3+ with the nitriles HCN, CH3CN, CH2CHCN, CH3CH2CN, CH2CHCH2CN, CH3CH2CH2CN, (CH3)2CHCN, C2N2, and CH2(CN)2. The reactions were studied using a selected-ion flow tube (SIFT) at 294 +/- 2 K and at a helium buffer gas pressure of 0.35 +/- 0.01 Torr and exhibited a wide range of chemical behavior. For the monocations C60.+ and C70.+, no detectable reaction occurred with any of the nitriles. For the dications C60(2+) and C70(2+), the only primary or secondary product channel evident in all instances was addition: tertiary association was seen to be considerably less efficient than the primary and secondary reactions, and the formation of a quadruple adduct C60(RCN)42+ was only detected in the reaction with butyronitrile, CH3CH2CH2CN. The observed primary rate coefficients show a very clear dependence upon the molecular complexity of the nitrile: association proceeds more efficiently for nitriles with a higher number of hydrogen atoms. This observation is explained in terms of a model which relates the number of C-H bonds-or, alternatively, the number of internal rotational modes-in the collision complex to the lifetime and probability of stabilization of this complex. For the trication C60.3+, addition was observed as the main primary product channel for all of the nitriles and was rapid for all nitriles except dicyanogen. Multiple adducts were observed in most instances, although in the reactions of tricationic adducts of acrylonitrile, allyl cyanide, malononitrile, and dicyanogen with the parent neutral, the dominant secondary product channel was a charge-separating ligand-transfer reaction resulting in the formation of a nitrile dimer cation (RCN)2.+. Proton transfer from a multiply-charged nitrile adduct to the parent nitrile was noted only in the case of C60(NCH).3+ + HCN. The consequences of the observed reactivity of C60.+ and C60(2+) for models of interstellar chemical evolution are discussed.