Publications

Pressure and temperature dependence of the reaction of vinyl radical with ethylene

Ismail, Huzeifa; Franklin Goldsmith, C.; Abel, Paul R.; Howe, Pui T.; Fahr, Askar; Halpern, Joshua B.; Jusinski, Leonard E.; Georgievskii, Yuri; Taatjes, Craig A.; Green, William H.

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C 2H 3 + C 2H 4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H 2C=CH) were generated by laser photolysis of vinyl iodide (C 2H 3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k = (7 ±1) × 10 -14 cm 3 molecule -1 s -1 (T/298 K) 2 exp[-(1430 ± 70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C 4H 7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl. © 2007 American Chemical Society.