Experimental and Theoretical Investigation of the Self-Reaction of Phenyl Radicals

Abstract

A combination of experiment and theory is applied to the self-reaction kinetics of phenyl radicals. The dissociation of phenyl iodide is observed with both time-of-flight mass spectrometry, TOF-MS, and laser schlieren, LS, diagnostics coupled to a diaphragmless shock tube for temperatures ranging from 1276 to 1853 K. The LS experiments were performed at pressures of 22 +/- 2, 54 +/- 7, and 122 +/- 6 Torr, and the TOF-MS experiments were performed at pressures in the range 500-700 Torr. These observations are sensitive to both the dissociation of phenyl iodide and to the subsequent self-reaction of the phenyl radicals. The experimental observations indicate that both these reactions are more complicated than previously assumed. The phenyl iodide dissociation yields approximately 6% C(6)H(4) + HI in addition to the major and commonly assumed C(6)H(5) + I channel. The self-reaction of phenyl radicals does not proceed solely by recombination, but also through disproportionation to benzene + o-/m-/p-benzynes, with comparable rate coefficients for both. The various channels in the self-reaction of phenyl radicals are studied with ab initio transition state theory based master equation calculations. These calculations elucidate the complex nature of the C(6)H(5) self-reaction and are consistent with the experimental observations. The theoretical predictions are used as a guide in the development of a model for the phenyl iodide pyrolysis that accurately reproduces the observed laser schlieren profiles over the full range of the observations.

Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures

“…The absence of other product isomers shows the selectivity of this process. A comparison to the work by Tranter et al 14 and by Shukla and Koshi is instructive, 12 who previously studied reactions of phenyl in much larger reactors. Both the EI mass spectrum 14 and the photoionization mass spectra 12 recorded at 1100 to 1200 K are very similar to the one presented above.…”

“…A comparison to the work by Tranter et al 14 and by Shukla and Koshi is instructive, 12 who previously studied reactions of phenyl in much larger reactors. Both the EI mass spectrum 14 and the photoionization mass spectra 12 recorded at 1100 to 1200 K are very similar to the one presented above. This shows that the properties of the SiC microreactor resemble those of the much larger reactors employed so far for studying high temperature reactions.…”

“…13 In a recent shock tube study employing iodobenzene as a precursor Tranter et al found that the direct dimerization of phenyl is accompanied by a disproportionation to benzene + benzyne with a comparable rate (I). 14 2 C 6 H 5 -C 6 H 6 + C 6 H 4 (I)…”

A wide range kinetic modeling study of pyrolysis and oxidation of benzene

“…The self-reaction between phenyl radicals has been recently investiga ted by [64][65][66]. Their theoretical results indicate the presence of a minor reaction channel leading to the formation of benzene and o-benzyne: Table 1. heavier species.…”

A shock tube with a high-repetition-rate time-of-flight mass spectrometer for investigations of complex reaction systems

“…IV and mass resolution) and data acquisition which was the main problem in the early studies. 8 In the past few years, Tranter et al 10,[13][14][15][16] published a series of papers introducing a new HRR-TOF-MS shock tube. One of the authors (S.D.)…”