Kinetics and mechanisms for the reactions of phenyl radical with ketene and its deuterated isotopomer: An experimental and theoretical study

Kinetics and wmechanism for the reaction of phenyl radical (C6H5) with ketene (H2Cbeta=C-alpha=O) were studied by the cavity ring-down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C6H5 transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD2CO, can be expressed by the Arrhenius equation k = (5.9 +/- 1.8) x 10(11) exp[-(1160 +/- 100)/T] cm(3) mol(-2) s(-1) over a temperature range of 301-474 K. <LF>The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6-31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C-alpha, C-beta, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298-2500 K under atmospheric pressure by using the predicted transition-state parameters and adjusted entrance reaction barriers E-alpha, E-beta - 1.2 kcal mol(-1); they can be represented by the following expression in units of cm(3) mol(-1) s(-1) k(alpha) -6.2 x 10(19) T-2.3 exp[ = 7590/T] and kbeta - 3.2 x 10(4) T-2.4 exp[-246/T].