Formation of Aromatic Structures from Chain Hydrocarbons in Electrical Discharges: Absorption and Fluorescence Study of C11H9+ and C11H9 center dot Isomers in Neon Matrices

A set of arenes (phenylacetylene, indene, and naphthalene cations and C11H9+ isomers) was produced from 2,4-hexadiyne diluted in helium in a hot-cathode discharge source. The mass-selected ions were codeposited with neon at 6 K and investigated by electronic absorption spectroscopy. This reveals that fused-ring species are readily formed from an acyclic precursor in such a source. After photobleaching of matrices containing C11H9+, neutral C11H9- radicals were also characterized. Assignment of the observed transitions to different m/z = 141 cationic and corresponding neutral isomers is given and supported by experiments using other precursors, fluorescence measurements, and time-dependent density functional and second-order approximate coupled cluster calculations.