Abstract
The chemistry of first aromatic ring, i.e., benzene (C6H6) and phenyl radial (C6H5), plays a key role in the growth of polycyclic aromatic hydrocarbons (PAHs) and ultimately soot formation. In this work, the self-recombination reaction of phenyl radicals was investigated over the temperature range of 950- 1300 K and pressures near 1 atm by employing shock tube and laser absorption diagnostics. Phenyl radical was generated by the rapid thermal unimolecular dissociation of nitrosobenzene (C6H5NO), a clean precursor of C6H5 radical. The reaction progress was monitored by detecting C6H5 and NO simultaneously using visible laser absorption near 445 nm and mid-IR laser absorption near 5.517 mu m, respectively. For the reaction C6H5NO -> C6H5 + NO (R 1 ), our data show an excellent agreement with earlier reports. The high-pressure limiting rate coefficient, by combining all available data, may be expressed as k infinity 1 (T(K) ) = 3.2 x 10(66) T-15.2 e(-37743/T) s(-1). This work reports the temperature dependence of the absorption cross-section of phenyl radical at 445 nm for first time. Our experiments indicate that the self-reaction of phenyl radicals yielding biphenyl, C6H5 + C6H5 -> C6H5C6H5 (R-2a), is a major channel. The rate coefficients of reaction (R-2a) show a weak temperature dependence with an average value of k(2a) = (6.91 +/- 0.42) x 10(12) cm(3) mol(-1) s(-1) in the temperature range of 950-1300 K. Our measured data, k(2a)(T, P = 1.1-1.5 atm), are found to be close to the high-pressure limiting rate coefficients. Combining with the literature low-temperature data, the self-recombination reaction of phenyl radicals may be expressed as k(2a)(infinity)(T = 300 - 1450 K ) = 2 . 8 x 10(17)T(-1.44)e(-540/T) cm(3) mol(-1) s(-1). The measurements of this study represent the first high-temperature direct experimental determination of the rate coefficients of this important prototype aromatic radical-radical reaction. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.