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 C₁₀H₇O ₂ 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) × 10¹¹ 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.