Kinetics of the Self Reaction of Cyclopentadienyl Radicals

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 119; no. 28; pp. 7418 - 7429
• Main Authors: Knyazev, Vadim D, Popov, Konstantin V
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.07.2015
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.5b00644

The kinetics of the self-reaction of cyclopentadienyl radicals (c-C5H5) was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 304–600 K and at bath gas densities of (3.00–12.0) × 1016 molecules cm–3. The room-temperature value of the rate constant, (3.98 ± 0.41) × 10–10 cm3 molecule–1 s–1, is significantly higher than the rate constants for most hydrocarbon radical–radical reactions and coincides with the estimated collision rate. The observed overall c-C5H5 + c-C5H5 rate constant demonstrates an unprecedented strong negative temperature dependence: k 1 = 2.9 × 10–12 exp­(+1489 K/T) cm3 molecule–1 s–1, with estimated uncertainty increasing with temperature, from 13% at 304 to 32% at 600 K. Formation of C10H10 as the primary product of cyclopentadienyl self-reaction was observed. In additional experiments performed at the temperature of 800 K, formation of C10H10, C10H9, and C10H8 was observed. Final product analysis by gas chromatography/mass spectrometry detected two isomers of C10H8 at 800 K: naphthalene (major) and azulene (minor).