Temperature and Pressure Effects in the Addition of H Atoms to Propylene

The effect of He pressure on the rate of addition of hydrogen atoms to propylene was measured at 298°K. H-atom concentration was measured by the method of resonance fluorescence of Lyman α radiation at 121.6 nm. The results are consistent with the 1 / p1/2 dependence of kbi recently observed in the H-atom–ethylene system. The limiting high-pressure rate constant obtained in this work is H+C3H6→C3H7, k1 = 1.61 ± 0.04 × 10−12cm3molecule−1·sec−1. The temperature dependence of the H-atom addition was investigated at 50 torr total pressure over the temperature range 177–473°K. Analysis of the data below room temperature gives the following Arrhenius parameters for addition to the terminal olefinic position: kbi50 = (10.18 ± 0.26) × 10−12exp[− (1211 ± 11) / 1.987T] cm3molecule−1·sec−1. Deviations from this dependence above 298°K can be assigned to nonterminal addition, H-atom abstraction, and increased decomposition of the excited propyl radicals.