High-temperature investigations on the pyrolysis of cyclopentadiene

The shock tube technique has been used to investigate high-temperature reactions of C₅-species, which appear to play an important role in polycyclic aromatic hydrocarbon (PAH) and soot formation. The unimolecular decomposition of cyclopentadiene (C₅H₆) has been studied behind reflected shock waves. The temperature ranged from 1260 to 1600 K at pressures between 0.7 and 5.6 bar. Initial cyclopentadiene concentrations ranged from 0.5 to 120 ppm, diluted in argon. Atomic Resonance Absorption Spectrometry (ARAS) was used to record the temporal concentration profiles of H-atoms during the pyrolysis of cyclopentadiene under very low concentration conditions. Absorption spectrometry and optical multichannel analyzer for the detection of acetylene during C₅H₆ pyrolysis were applied. For the main channel of cyclopentadiene decomposition C₅H₆→C₅H-c+H (R1) a revised rate expression of k₁=4.0×10¹⁴×exp(−38760/T) s⁻¹ was deduced, after reevaluation of the previous experiments with an improved experimental calibration curve. For evaluating the decay rate of the cyclopentadienyl radical C₅H₅-c→C₂H₂+C₃H₃ (R3) PUMP2 level calculations were performed. The results were validated by means of the measured C₂H₂-and H-absorption profiles. Theory and experiments presented in this work verify quantitatively the decomposition process of the C₅H₅-c radical.