Reactions of 1-Naphthyl Radicals with Acetylene. Single-Pulse Shock Tube Experiments andQuantum Chemical Calculations. Differences and Similarities in the Reaction with Ethylene

摘要

The reactions of 1-naphthyl radicals with acetylene were studied behind reflected shock waves in a single-pulse shock tube, covering the temperature range 950-1200 K at overall densities behind the reflected shocksof -2.5 x 10-5 mol/cm3. 1-Iodonaphthalene served as the source for 1-naphthyl radicals. The [acetylene]/[1-iodonaphthalene] ratio in all of the experiments was -100 to channel the free radicals into reactions withacetylene rather than iodonaphthalene. Only two major products resulting from the reactions of 1-naphthylradicals with acetylene and with hydrogen atoms were found in the post shock samples. They wereacenaphthylene and naphthalene. Some low molecular weight aliphatic products at rather low concentrations,resulting from an attack of various free radicals on acetylene, were also found in the shocked samples. Inview of the relatively low temperatures employed in the present experiments, the unimolecular decompositionrate of acetylene is negligible. One potential energy surface describes the production of acenaphthylene and1-naphthyl acetylene, although the latter was not found experimentally due to the high barrier (calculated)required for its production. Using quantum chemical methods, the rate constants for three unimolecularelementary steps on the surface were calculated using transition state theory. A kinetics scheme containing16 elementary steps was constructed, and computer modeling was performed. An excellent agreement betweenthe experimental yields of the two major products and the calculated yields was obtained. Differences andsimilarities in the potential energy surfaces of 1-naphthyl radical + acetylene and those of ethylene arepresented, and the kinetics mechanisms are discussed.