Reactions of carbon cluster ions with small hydrocarbons

The ion/molecule reactions of laser-generated carbon cluster ions, C+n (n=3–20), with the neutral hydrocarbons CH4, C2H2, and C2H4 are studied using Fourier transform mass spectrometry. Branching ratios and rate constants are reported for the observed reactions. The reactions and proposed mechanisms are consistent with previous results and suggest a structural change of the cluster ions from linear to cyclic between n=9 and 10. The proposed reaction mechanisms include carbene insertion into both the C–H bonds and the unsaturated C–C bonds of the reactant neutrals. The reactions of the cluster ions with the unsaturated hydrocarbons C2H2 and C2H4 are the first systems in which the cyclic (n≥10) cluster ions are reactive. The results of the reactivity of the carbon cluster ions with the carbon-containing neutrals are discussed in terms of the stability of the clusters toward carbon atom addition and cluster growth. Further evidence is reported for the presence of structural isomers (linear and cyclic) of C+7 including a novel reaction sequence used to remove the linear isomer so that the reactivity of the cyclic isomer with C2H2 may be studied independently.