Reaction of hydrogen atoms with cyclopropane in the temperature range 358–550 K

Abstract

The reaction of hydrogen atoms with cyclopropane (CP) has been investigated at a helium pressure of ca. 5 Torr in the temperature range 358–550 K using a conventional flow-discharge system coupled to a quadrupole mass spectrometer. Two sets of pseudo-first-order experiments were performed: (i) where [CP]≫[H], in which case decay of [H] was measured, and (ii) where [CP]≪[H], in which case formation of CH₄, the predominant hydrocarbon product, was measured. To evaluate the rate constant k₁ H + c-C₃H₆→ H₂+ c-C₃H₅(1) computer integration of a detailed mechanism for the overall process has been carried out. We obtain self-consistent values of k₁ represented by log (k₁/cm³ mol^–1 s^–1)= 14.21 ± 0.13 –(49.0 ± 1.1 kJ mol^–1)/(2.3 RT) which are in accord with the ‘high’ value, 445 kJ mol^–1, for the C—H bond dissociation energy in cyclopropane. There is no evidence of curvature in the Arrhenius plot over the range 358–550 K.