Isomers of Small Carbon Cluster Anions: Linear Chains with up to 20 Atoms

Abstract

The structure of small carbon cluster anions, C_n^- (4 ≤ n ≤ 20), was investigated with the use of ion chromatography. With this technique, both the existence and the relative amounts of possible structural isomers can be determined. More than 99% of the ions C₅^- to C₉^- were found to be linear under these experimental conditions. Starting with C₁₀^-, a monocyclic isomer was observed, and linear and moncyclic structures coexisted from C₁₀^- through at least C₂₀^-. This result is in contrast to previous work on positive ions, which showed the existence of linear isomers from C₅⁺ to C₁₀⁺, with linear and cyclic isomers coexisting only from C₇⁺ to C₁₀⁺. Above C₁₀⁺, no linear clusters were observed.