Kinetics of the C6H5 + O2 Reaction at Low Temperatures

Abstract

The kinetics of the C[sub 6]H[sub 5] + O[sub 2] reaction has been studied with the cavity-ring-down (CRD) method by monitoring the rate of C[sub 6]H[sub 5]O[sub 2] radical formation at 496.4 nm. The second-order rate constants measured under the conditions, 20 Torr [le] P [le] 80 Torr (Ar), 297 K [le] T [le] 473 K, were found to be pressure-independent, with a small negative activation of 0.32 kcal/mol. Under the conditions employed in the present work, the C[sub 6]H[sub 5] + O[sub 2] reaction takes place primarily by the addition-stabilization process C[sub 6]H[sub 5] + O[sub 2] [yields] C[sub 6]H[sub 5]O[sub 2] (+M) [yields] C[sub 6]H[sub 5]O[sub 2]. A search carried out at 575.4 nm for the production of C[sub 6]H[sub 5]O, which could be conveniently and sensitively detected by the CRD method, failed to detect the radical. This finding is fully consistent with the apparent large activation energy for the formation of C[sub 6]H[sub 5]O from the C[sub 6]H[sub 5] + O[sub 2] reaction (6 kcal/mol) recently reported by Frank and co-workers (ref 30) using the atomic resonance absorption-shock tube method at T > 900 K. 38 refs., 6 figs., 3 tabs.