Reaction of hydrogen atoms with propane in the temperature range 298–534 K

Abstract

The reaction of hydrogen atoms with propane has been investigated at a helium pressure of ca. 5 Torr in the temperature range 298–534 K using a conventional flow-discharge system coupled to a quadrupole mass spectrometer. Two sets of pseudo-first-order experiments were performed: (i) where [C₃H₈][H], in which case decay of [H] was measured, and (ii) where [C₃H₈][H], in which case formation of CH₄ was measured.

In order to evaluate the rate constant, k₁, of the reaction assumptions concerning the stoichiometry of the overall process have to be made. It is shown that previous assumptions are wrong. We have used computer integration of a detailed mechanism for the overall process to evaluate self-consistent values of k₁ from our experimental data. We obtain the Arrhenius parameters log (k₁/cm³ mol^–1 s^–1)=(13.81 ± 0.07)–(28.8±0.6) kJ mol^–1/2.3 RT from our results for T 370 K. At lower temperatures there is evidence for curvature of the Arrhenius plot and the activation energy drops to 21.8±1.8 kJ mol^–1 for temperatures < 370 K.