Kinetic study of the 2-naphthyl (C10H7) radical reaction with C2H2

The kinetics for the gas-phase reaction of 2-naphthyl radical with acetylene has been measured by monitoring the C10H7O2 radical in the visible region employing cavity ringdown spectrometry (CRDS) using 2-C10H7Br as a radical source photolyzing at 193 nm in the presence of a small fixed amount of O2 at 40 Torr pressure with Ar as a diluent. Absolute rate constants measured at temperatures between 303 and 448 K can be expressed by the following Arrhenius equation: k(T) = (3.36 +/- 0.63) x 10(11) exp[-(817 +/- 34)/T] cm3 mol(-1) s(-1). Theoretically, the potential energy surfaces (PESs) for the reactions of acetylene with 1- and 2-C10H7 radicals have been calculated with the G2MS//B3LYP/6-311+G(d,p) method. The PESs show that the reactions of 1- and 2-C10H7 with C2H2 occur first by forming adducts with 2.6 and 2.9 kcal/mol barriers, respectively. The rate constants for the stabilization and decomposition of the adducts have been predicted by RRKM/ME calculations. The mechanisms for the decomposition of the two adducts were predicted to be distinctively different under experimental conditions; the excited 1-C10H7C2H2 radical produces primarily acenaphthylene because of its low formation barrier, while the excited 2-C10H7C2H2 radical can be effectively stabilized by collisional quenching due to its high exit barrier. The predicted rate constant for the 2-C10H7 reaction with C2H2 is in reasonable agreement with the experimental values under the conditions employed.