Electronic spectra and molecular geometry of the non-linear carbon chain C9H3

Two electronic bands at ∼18 881 and ∼18 920 cm−1 – previously assigned to the carbon chain molecule C9H3 – have been recorded, resolving for the first time their K-stack structure. The C9H3 radicals are produced by discharging and expanding a diluted gas mixture of acetylene in helium employing a pulsed pinhole nozzle. Cavity ring-down spectroscopy is used to record spectra in direct absorption. The improved experimental data and spectrum simulations based on new theoretical structure predictions show that the HC4(CH)C4H isomer (with C2v symmetry) is a likely carrier of the two observed C9H3 bands.